Fix enumerator disposal when cancellation outside of serialization occurs.

[eiriktsarpalis]

Fix #120010.

[Copilot]

Pull Request Overview

This PR fixes a bug where enumerator disposal was not happening correctly when cancellation occurs outside of serialization, specifically addressing issue #120010. The fix ensures proper cleanup of enumerators when serialization is cancelled by external cancellation tokens.

Key changes:

• Added cancellation token parameters to all serialization wrapper methods to support proper cancellation handling
• Fixed disposal logic in WriteStack to prevent double disposal and handle null stack cases
• Added comprehensive regression tests for both sync and async enumerable cancellation scenarios

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
JsonSerializerWrapper.Reflection.cs	Added CancellationToken parameters to all async serialization methods and updated calls to pass tokens through
JsonSerializerWrapper.SourceGen.cs	Added CancellationToken parameters to source generation wrapper methods
CollectionTests.cs	Added JsonSerializable attribute for new test type
StreamingJsonSerializerWrapper.cs	Updated abstract method signatures to include CancellationToken parameters
PipeJsonSerializerWrapper.cs	Updated abstract method signatures to include CancellationToken parameters
CollectionTests.Generic.Write.cs	Added regression test for enumerable cancellation with disposal verification
AsyncEnumerableTests.cs	Added regression test for async enumerable cancellation with disposal verification
WriteStack.cs	Fixed disposal logic to prevent double disposal and handle edge cases with null stack

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[eiriktsarpalis]

/ba-g test failures unrelated.