chore: rework NatsOpt.Default initialization

[regnrat]

Creating NatsOpts.Default with sub property default objects:

• WebSocketOpts = NatsWebSocketOpts.Default,
• TlsOpts = NatsTlsOpts.Default,
• AuthOpts = NatsAuthOpts.Default,

Using default constructors for these sub properties in default constructor of NatsOpts.
Closes #920

[mtmk]

thanks @regnrat. Looking good. Are there any cases you can think of this might break an existing app?

edit: if we think it might break existing apps in any way we can change the base to 2.7 release branch.

[regnrat]

I think you can construct situations where this breaks an application, in theory. But that would require unclean code on the consumers side and wouldn't make any sense.

But theoretical yes. Shall I change the base?

[mtmk]

I think you can construct situations where this breaks an application, in theory. But that would require unclean code on the consumers side and wouldn't make any sense.

But theoretical yes. Shall I change the base?

Yes, i think we should. we've been using minor version updates to signal potentially breaking API changes.

[Copilot]

Pull Request Overview

This PR refactors the initialization of NatsOpts.Default to use sub-property default objects while changing the default constructor to create new instances of sub-properties. This ensures proper object isolation when binding configurations to different NatsOpts instances.

• Changes NatsOpts.Default to explicitly set sub-properties to their respective static defaults
• Updates default constructor property initializers to use new() instead of static defaults
• Adds comprehensive tests to verify object isolation and configuration binding behavior

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/NATS.Client.Core/NatsOpts.cs	Restructures NatsOpts.Default initialization and updates constructor property defaults
tests/NATS.Client.CoreUnit.Tests/OptsTests.cs	Adds new test class with tests for default equivalence and configuration binding isolation
tests/NATS.Client.CoreUnit.Tests/NATS.Client.CoreUnit.Tests.csproj	Adds Microsoft.Extensions.Configuration packages for configuration binding tests

Comments suppressed due to low confidence (1)

tests/NATS.Client.CoreUnit.Tests/OptsTests.cs:4

• The class name 'OptsUrlTests' is misleading as the tests are about NatsOpts behavior, not URL-specific functionality. Consider renaming to 'NatsOptsTests' or 'OptsTests' to better reflect the actual test content.

public class OptsUrlTests

[mtmk]

LGTM thanks @regnrat