Add ConfigureAwaitOptions polyfill for pre-net8.0

 Closes #527

 - Add ConfigureAwaitOptions [Flags] enum with None,
   ContinueOnCapturedContext, SuppressThrowing, and ForceYielding
 - Add Task.ConfigureAwait(ConfigureAwaitOptions) extension method
 - Add Task<TResult>.ConfigureAwait(ConfigureAwaitOptions) extension method
 - Task<TResult> rejects SuppressThrowing (matches BCL behavior)
 - Invalid flag combinations throw ArgumentOutOfRangeException
 - ForceYielding implemented via Task.Yield() wrapper
 - SuppressThrowing implemented via try/catch wrapper
 - Restructure Polyfill_Task.cs to use inner #if guards
 - Add tests, consumption usage, and Split files

src/Consume/Consume.cs

@@ -1400,6 +1400,13 @@ void Task_Methods()
         new Task<int>(func).WaitAsync(CancellationToken.None);
         new Task<int>(func).WaitAsync(TimeSpan.Zero);
         new Task<int>(func).WaitAsync(TimeSpan.Zero, CancellationToken.None);
+        Task.CompletedTask.ConfigureAwait(ConfigureAwaitOptions.None);
+        Task.CompletedTask.ConfigureAwait(ConfigureAwaitOptions.ContinueOnCapturedContext);
+        Task.CompletedTask.ConfigureAwait(ConfigureAwaitOptions.SuppressThrowing);
+        Task.CompletedTask.ConfigureAwait(ConfigureAwaitOptions.ForceYielding);
+        Task.FromResult(0).ConfigureAwait(ConfigureAwaitOptions.None);
+        Task.FromResult(0).ConfigureAwait(ConfigureAwaitOptions.ContinueOnCapturedContext);
+        Task.FromResult(0).ConfigureAwait(ConfigureAwaitOptions.ForceYielding);
     }
 
 #if FeatureMemory

src/Polyfill/ConfigureAwaitOptions.cs

@@ -0,0 +1,44 @@
+#if !NET8_0_OR_GREATER
+
+namespace System.Threading.Tasks;
+
+/// <summary>
+/// Options to control behavior when awaiting.
+/// </summary>
+//Link: https://learn.microsoft.com/en-us/dotnet/api/system.threading.tasks.configureawaitoptions?view=net-11.0
+[Flags]
+#if PolyUseEmbeddedAttribute
+[global::Microsoft.CodeAnalysis.EmbeddedAttribute]
+#endif
+#if PolyPublic
+public
+#endif
+enum ConfigureAwaitOptions
+{
+    /// <summary>
+    /// No options specified.
+    /// </summary>
+    None = 0,
+
+    /// <summary>
+    /// Attempts to marshal the continuation back to the original <see cref="System.Threading.SynchronizationContext"/>
+    /// or <see cref="System.Threading.Tasks.TaskScheduler"/> present on the originating thread at the time of the await.
+    /// </summary>
+    ContinueOnCapturedContext = 1,
+
+    /// <summary>
+    /// Avoids throwing an exception at the completion of awaiting a <see cref="Task"/> that ends
+    /// in the <see cref="TaskStatus.Faulted"/> or <see cref="TaskStatus.Canceled"/> state.
+    /// </summary>
+    SuppressThrowing = 2,
+
+    /// <summary>
+    /// Forces an await on an already completed <see cref="Task"/> to behave as if the <see cref="Task"/>
+    /// wasn't yet completed, such that the current asynchronous method will be forced to yield its execution.
+    /// </summary>
+    ForceYielding = 4
+}
+
+#else
+[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Threading.Tasks.ConfigureAwaitOptions))]
+#endif

src/Polyfill/Polyfill_Task.cs

@@ -107,3 +107,81 @@ public static async Task<TResult> WaitAsync<TResult>(
 }
 
 #endif
+#if !NET8_0_OR_GREATER
+
+    /// <summary>Configures an awaiter used to await this <see cref="Task"/>.</summary>
+    //Link: https://learn.microsoft.com/en-us/dotnet/api/system.threading.tasks.task.configureawait?view=net-11.0#system-threading-tasks-task-configureawait(system-threading-tasks-configureawaitoptions)
+    public static ConfiguredTaskAwaitable ConfigureAwait(this Task target, ConfigureAwaitOptions options)
+    {
+        if ((options & ~(ConfigureAwaitOptions.ContinueOnCapturedContext |
+                         ConfigureAwaitOptions.SuppressThrowing |
+                         ConfigureAwaitOptions.ForceYielding)) != 0)
+        {
+            throw new ArgumentOutOfRangeException(nameof(options));
+        }
+
+        var task = target;
+
+        if ((options & ConfigureAwaitOptions.ForceYielding) != 0)
+        {
+            task = ForceYieldAsync(task);
+
+            static async Task ForceYieldAsync(Task t)
+            {
+                await Task.Yield();
+                await t;
+            }
+        }
+
+        if ((options & ConfigureAwaitOptions.SuppressThrowing) != 0)
+        {
+            task = SuppressThrowAsync(task);
+
+            static async Task SuppressThrowAsync(Task t)
+            {
+                try
+                {
+                    await t;
+                }
+                catch
+                {
+                }
+            }
+        }
+
+        return task.ConfigureAwait(
+            (options & ConfigureAwaitOptions.ContinueOnCapturedContext) != 0);
+    }
+
+    /// <summary>Configures an awaiter used to await this <see cref="Task{TResult}"/>.</summary>
+    //Link: https://learn.microsoft.com/en-us/dotnet/api/system.threading.tasks.task-1.configureawait?view=net-11.0#system-threading-tasks-task-1-configureawait(system-threading-tasks-configureawaitoptions)
+    public static ConfiguredTaskAwaitable<TResult> ConfigureAwait<TResult>(
+        this Task<TResult> target,
+        ConfigureAwaitOptions options)
+    {
+        if ((options & ~(ConfigureAwaitOptions.ContinueOnCapturedContext |
+                         ConfigureAwaitOptions.ForceYielding)) != 0)
+        {
+            throw new ArgumentOutOfRangeException(nameof(options));
+        }
+
+        var task = target;
+
+        if ((options & ConfigureAwaitOptions.ForceYielding) != 0)
+        {
+            task = ForceYieldAsync(task);
+
+            static async Task<TResult> ForceYieldAsync(Task<TResult> t)
+            {
+                await Task.Yield();
+                return await t;
+            }
+        }
+
+        return task.ConfigureAwait(
+            (options & ConfigureAwaitOptions.ContinueOnCapturedContext) != 0);
+    }
+
+#endif
+}
+

src/Split/net461/ConfigureAwaitOptions.cs

@@ -0,0 +1,35 @@
+// <auto-generated />
+#pragma warning disable
+namespace System.Threading.Tasks;
+/// <summary>
+/// Options to control behavior when awaiting.
+/// </summary>
+[System.Flags]
+#if PolyUseEmbeddedAttribute
+[global::Microsoft.CodeAnalysis.EmbeddedAttribute]
+#endif
+#if PolyPublic
+public
+#endif
+enum ConfigureAwaitOptions
+{
+    /// <summary>
+    /// No options specified.
+    /// </summary>
+    None = 0,
+    /// <summary>
+    /// Attempts to marshal the continuation back to the original <see cref="System.Threading.SynchronizationContext"/> or
+    /// <see cref="System.Threading.Tasks.TaskScheduler"/> present on the originating thread at the time of the await.
+    /// </summary>
+    ContinueOnCapturedContext = 1,
+    /// <summary>
+    /// Avoids throwing an exception at the completion of awaiting a <see cref="Task"/> that ends in the
+    /// <see cref="TaskStatus.Faulted"/> or <see cref="TaskStatus.Canceled"/> state.
+    /// </summary>
+    SuppressThrowing = 2,
+    /// <summary>
+    /// Forces an await on an already completed <see cref="Task"/> to behave as if the <see cref="Task"/> wasn't yet
+    /// completed, such that the current asynchronous method will be forced to yield its execution.
+    /// </summary>
+    ForceYielding = 4
+}

src/Split/net461/Polyfill_Task.cs

@@ -82,4 +82,63 @@ public static async Task<TResult> WaitAsync<TResult>(
 		await ((Task) target).WaitAsync(timeout, cancellationToken);
 		return target.Result;
 	}
+    /// <summary>Configures an awaiter used to await this <see cref="Task"/>.</summary>
+    public static System.Runtime.CompilerServices.ConfiguredTaskAwaitable ConfigureAwait(this Task target, ConfigureAwaitOptions options)
+    {
+        if ((options & ~(ConfigureAwaitOptions.ContinueOnCapturedContext |
+                         ConfigureAwaitOptions.SuppressThrowing |
+                         ConfigureAwaitOptions.ForceYielding)) != 0)
+        {
+            throw new System.ArgumentOutOfRangeException(nameof(options));
+        }
+        var task = target;
+        if ((options & ConfigureAwaitOptions.ForceYielding) != 0)
+        {
+            task = ForceYieldAsync(task);
+            static async Task ForceYieldAsync(Task t)
+            {
+                await Task.Yield();
+                await t;
+            }
+        }
+        if ((options & ConfigureAwaitOptions.SuppressThrowing) != 0)
+        {
+            task = SuppressThrowAsync(task);
+            static async Task SuppressThrowAsync(Task t)
+            {
+                try
+                {
+                    await t;
+                }
+                catch
+                {
+                }
+            }
+        }
+        return task.ConfigureAwait(
+        (options & ConfigureAwaitOptions.ContinueOnCapturedContext) != 0);
+    }
+    /// <summary>Configures an awaiter used to await this <see cref="Task{TResult}"/>.</summary>
+    public static System.Runtime.CompilerServices.ConfiguredTaskAwaitable<TResult> ConfigureAwait<TResult>(
+        this Task<TResult> target,
+        ConfigureAwaitOptions options)
+    {
+        if ((options & ~(ConfigureAwaitOptions.ContinueOnCapturedContext |
+                         ConfigureAwaitOptions.ForceYielding)) != 0)
+        {
+            throw new System.ArgumentOutOfRangeException(nameof(options));
+        }
+        var task = target;
+        if ((options & ConfigureAwaitOptions.ForceYielding) != 0)
+        {
+            task = ForceYieldAsync(task);
+            static async Task<TResult> ForceYieldAsync(Task<TResult> t)
+            {
+                await Task.Yield();
+                return await t;
+            }
+        }
+        return task.ConfigureAwait(
+        (options & ConfigureAwaitOptions.ContinueOnCapturedContext) != 0);
+    }
 }

src/Split/net462/ConfigureAwaitOptions.cs

@@ -0,0 +1,35 @@
+// <auto-generated />
+#pragma warning disable
+namespace System.Threading.Tasks;
+/// <summary>
+/// Options to control behavior when awaiting.
+/// </summary>
+[System.Flags]
+#if PolyUseEmbeddedAttribute
+[global::Microsoft.CodeAnalysis.EmbeddedAttribute]
+#endif
+#if PolyPublic
+public
+#endif
+enum ConfigureAwaitOptions
+{
+    /// <summary>
+    /// No options specified.
+    /// </summary>
+    None = 0,
+    /// <summary>
+    /// Attempts to marshal the continuation back to the original <see cref="System.Threading.SynchronizationContext"/> or
+    /// <see cref="System.Threading.Tasks.TaskScheduler"/> present on the originating thread at the time of the await.
+    /// </summary>
+    ContinueOnCapturedContext = 1,
+    /// <summary>
+    /// Avoids throwing an exception at the completion of awaiting a <see cref="Task"/> that ends in the
+    /// <see cref="TaskStatus.Faulted"/> or <see cref="TaskStatus.Canceled"/> state.
+    /// </summary>
+    SuppressThrowing = 2,
+    /// <summary>
+    /// Forces an await on an already completed <see cref="Task"/> to behave as if the <see cref="Task"/> wasn't yet
+    /// completed, such that the current asynchronous method will be forced to yield its execution.
+    /// </summary>
+    ForceYielding = 4
+}

src/Split/net462/Polyfill_Task.cs

@@ -82,4 +82,63 @@ public static async Task<TResult> WaitAsync<TResult>(
 		await ((Task) target).WaitAsync(timeout, cancellationToken);
 		return target.Result;
 	}
+    /// <summary>Configures an awaiter used to await this <see cref="Task"/>.</summary>
+    public static System.Runtime.CompilerServices.ConfiguredTaskAwaitable ConfigureAwait(this Task target, ConfigureAwaitOptions options)
+    {
+        if ((options & ~(ConfigureAwaitOptions.ContinueOnCapturedContext |
+                         ConfigureAwaitOptions.SuppressThrowing |
+                         ConfigureAwaitOptions.ForceYielding)) != 0)
+        {
+            throw new System.ArgumentOutOfRangeException(nameof(options));
+        }
+        var task = target;
+        if ((options & ConfigureAwaitOptions.ForceYielding) != 0)
+        {
+            task = ForceYieldAsync(task);
+            static async Task ForceYieldAsync(Task t)
+            {
+                await Task.Yield();
+                await t;
+            }
+        }
+        if ((options & ConfigureAwaitOptions.SuppressThrowing) != 0)
+        {
+            task = SuppressThrowAsync(task);
+            static async Task SuppressThrowAsync(Task t)
+            {
+                try
+                {
+                    await t;
+                }
+                catch
+                {
+                }
+            }
+        }
+        return task.ConfigureAwait(
+        (options & ConfigureAwaitOptions.ContinueOnCapturedContext) != 0);
+    }
+    /// <summary>Configures an awaiter used to await this <see cref="Task{TResult}"/>.</summary>
+    public static System.Runtime.CompilerServices.ConfiguredTaskAwaitable<TResult> ConfigureAwait<TResult>(
+        this Task<TResult> target,
+        ConfigureAwaitOptions options)
+    {
+        if ((options & ~(ConfigureAwaitOptions.ContinueOnCapturedContext |
+                         ConfigureAwaitOptions.ForceYielding)) != 0)
+        {
+            throw new System.ArgumentOutOfRangeException(nameof(options));
+        }
+        var task = target;
+        if ((options & ConfigureAwaitOptions.ForceYielding) != 0)
+        {
+            task = ForceYieldAsync(task);
+            static async Task<TResult> ForceYieldAsync(Task<TResult> t)
+            {
+                await Task.Yield();
+                return await t;
+            }
+        }
+        return task.ConfigureAwait(
+        (options & ConfigureAwaitOptions.ContinueOnCapturedContext) != 0);
+    }
 }

src/Split/net47/ConfigureAwaitOptions.cs

@@ -0,0 +1,35 @@
+// <auto-generated />
+#pragma warning disable
+namespace System.Threading.Tasks;
+/// <summary>
+/// Options to control behavior when awaiting.
+/// </summary>
+[System.Flags]
+#if PolyUseEmbeddedAttribute
+[global::Microsoft.CodeAnalysis.EmbeddedAttribute]
+#endif
+#if PolyPublic
+public
+#endif
+enum ConfigureAwaitOptions
+{
+    /// <summary>
+    /// No options specified.
+    /// </summary>
+    None = 0,
+    /// <summary>
+    /// Attempts to marshal the continuation back to the original <see cref="System.Threading.SynchronizationContext"/> or
+    /// <see cref="System.Threading.Tasks.TaskScheduler"/> present on the originating thread at the time of the await.
+    /// </summary>
+    ContinueOnCapturedContext = 1,
+    /// <summary>
+    /// Avoids throwing an exception at the completion of awaiting a <see cref="Task"/> that ends in the
+    /// <see cref="TaskStatus.Faulted"/> or <see cref="TaskStatus.Canceled"/> state.
+    /// </summary>
+    SuppressThrowing = 2,
+    /// <summary>
+    /// Forces an await on an already completed <see cref="Task"/> to behave as if the <see cref="Task"/> wasn't yet
+    /// completed, such that the current asynchronous method will be forced to yield its execution.
+    /// </summary>
+    ForceYielding = 4
+}