[Extensions.AWS] Fix sampling behaviour for .NET 11 compatibility

[martincostello]

Changes

Fix sampling behaviour to be compatible with ActivityTraceFlags.RandomTraceId in .NET 11 (dotnet/runtime#124509).

OpenTelemetry.Extensions.AWS doesn't directly reference System.DiagnosticSource and the relevant code only targets .NET Framework so Activity.HasRandomizedTraceId can't be referenced in the code, but if the flag were set by other code the current approach would clobber the flag.

This refactors to leave the original flags as-is, then turn off ActivityTraceFlags.Recorded if needed.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 75.69%. Comparing base (f707627) to head (a93c779).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...OpenTelemetry.Extensions.AWS/AWSXRayIdGenerator.cs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4396   +/-   ##
=======================================
  Coverage   75.69%   75.69%           
=======================================
  Files         456      456           
  Lines       18246    18246           
=======================================
  Hits        13811    13811           
  Misses       4435     4435           

Flag	Coverage Δ
unittests-Instrumentation.AWS	85.22% <0.00%> (ø)

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

Files with missing lines	Coverage Δ
...OpenTelemetry.Extensions.AWS/AWSXRayIdGenerator.cs	58.33% <0.00%> (ø)

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[Copilot]

Pull request overview

Fixes the AWS X-Ray ID generator sampling logic so it preserves trace flags (including the new ActivityTraceFlags.RandomTraceId added in .NET 11) instead of clobbering them by resetting to None. Instead of clearing all flags and re-adding Recorded when sampled, the code now selectively toggles only the Recorded bit.

Changes:

• Removed the activity.ActivityTraceFlags = ActivityTraceFlags.None; reset in UpdateSamplingDecision.
• Added an else branch that clears only the Recorded flag (&= ~ActivityTraceFlags.Recorded) when sampling result is not AllDataAndRecorded.
• Added a CHANGELOG entry referencing PR #4396.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/OpenTelemetry.Extensions.AWS/AWSXRayIdGenerator.cs	Preserve unrelated trace flags by toggling only the Recorded bit instead of resetting all flags.
src/OpenTelemetry.Extensions.AWS/CHANGELOG.md	Document the .NET 11 sampling compatibility fix.

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