Add polyfill for TaskCompletionSource<T>.SetCanceled(...)

[Tyrrrz]

No description provided.

[Copilot]

Pull Request Overview

This PR adds a polyfill for TaskCompletionSource<T>.SetCanceled(CancellationToken) to enable this .NET 5.0+ API on older framework versions.

• Implements SetCanceled(CancellationToken) extension method for TaskCompletionSource<T>
• Adds comprehensive test coverage for both successful cancellation and error cases
• Updates existing NetCore10 tests to verify the TrySetCanceled return value

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
PolyShim/Net50/TaskCompletionSource.cs	Adds polyfill implementation that wraps TrySetCanceled with exception handling
PolyShim.Tests/Net50/TaskCompletionSourceTests.cs	Adds tests for the new SetCanceled method
PolyShim.Tests/NetCore10/TaskCompletionSourceTests.cs	Enhances existing tests to capture and verify TrySetCanceled return values

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (6d92f27) to head (76d4b07).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@     Coverage Diff      @@
##   master   #31   +/-   ##
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