Alpha fixes and improvements

[martintmk]

Details on the issue fix or feature implementation

Fixes and improvements based on some testing and playing with the alpha1 package.

• Timeout strategy disposing CancellationTokenSource too late
• ResultFormatter not being used for resilience events.
• The hedging should not dispose the resources it holds in background. It should do it as a post-execute action.
• Unifying the predicate arguments, all have the same <Strategy>PredicateArguments pattern. The delegate's name is always ShouldHandle.
• Setting default ShouldHandle callback for fallback.
• Changing argument structs for resilience events to classes. These were boxed anyway and we can still turn the pooling later one. All these are not executed on the hot path, only when resilience event occurs.
• Stack trace was missing for some exceptions.

Contributes to #1301

Confirm the following

• I started this PR by branching from the head of the default branch
• I have targeted the PR to merge into the default branch
• I have included unit tests for the issue/feature
• I have successfully run a local build

[martincostello]

Any tests we can add/extend to verify stack traces don't get lost?

[codecov]

Codecov Report

Merging #1319 (d845536) into main (5c341d5) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1319   +/-   ##
=======================================
  Coverage   83.37%   83.37%           
=======================================
  Files         264      268    +4     
  Lines        6333     6335    +2     
  Branches     1001     1001           
=======================================
+ Hits         5280     5282    +2     
  Misses        844      844           
  Partials      209      209           

Flag	Coverage Δ
macos	83.37% <100.00%> (+<0.01%)	⬆️
windows	83.37% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...c/Polly.Core/Utils/ReloadableResilienceStrategy.cs	100.00% <ø> (ø)
src/Polly.Core/Utils/TypeNameFormatter.cs	100.00% <ø> (ø)
...ependencyInjection/PollyDependencyInjectionKeys.cs	100.00% <ø> (ø)
...re/CircuitBreaker/CircuitBreakerStrategyOptions.cs	100.00% <100.00%> (ø)
...ircuitBreaker/Controller/CircuitStateController.cs	100.00% <100.00%> (ø)
...ly.Core/CircuitBreaker/OnCircuitClosedArguments.cs	100.00% <100.00%> (ø)
...ore/CircuitBreaker/OnCircuitHalfOpenedArguments.cs	100.00% <100.00%> (ø)
...ly.Core/CircuitBreaker/OnCircuitOpenedArguments.cs	100.00% <100.00%> (ø)
src/Polly.Core/Fallback/FallbackHandler.cs	100.00% <100.00%> (ø)
.../Polly.Core/Fallback/FallbackResilienceStrategy.cs	100.00% <100.00%> (ø)
... and 25 more

[martincostello]

Is there a specific issue we could link to?

[martintmk]

This one for example;
coverlet-coverage/coverlet#1284

There are more of those related to await handling