Emit warning when TraceIdRatioBasedSampler is used as child sampler

[Gosling-dude]

What does this change do?

• Emits a WARNING when TraceIdRatioBasedSampler is configured as a child sampler via ParentBasedSamplerBuilder.
• Warning is logged once at configuration time only.
• No runtime or sampling behavior is changed.

Why is this needed?

• Required by the OpenTelemetry trace SDK specification.
• Using TraceIdRatioBasedSampler as a child sampler can lead to unexpected behavior.

Implementation notes:

• Warning logic lives only in ParentBasedSamplerBuilder.
• ParentBasedSampler remains behavior-only with no logging or side effects.

How was this tested?

• ./gradlew :sdk:trace:test
• ./gradlew spotlessCheck

Closes #7790

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: Gosling-dude / name: Sumit Chauhan (49677d9, 4af9078, 64e09bc, db30494, e944463, ef83131, efdcb79)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.10%. Comparing base (1093571) to head (efdcb79).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #7937   +/-   ##
=========================================
  Coverage     90.09%   90.10%           
- Complexity     7432     7438    +6     
=========================================
  Files           834      834           
  Lines         22537    22546    +9     
  Branches       2236     2236           
=========================================
+ Hits          20304    20314   +10     
  Misses         1532     1532           
+ Partials        701      700    -1     

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[Gosling-dude]

All required checks are passing.

This implements the spec-required compatibility warning for TraceIdRatioBasedSampler when used as a child sampler. Logging is limited to ParentBasedSamplerBuilder and does not affect sampling behavior.

Happy to adjust if there are any suggestions.

[jkwatson]

This is generally only going to be done once for a given builder instance. I don't think we need the extra checks to make sure it only gets logged once.

[Gosling-dude]

That makes sense - agreed.

I’ll remove the warned* guards and emit the warning unconditionally when a TraceIdRatioBasedSampler is set as a child sampler. That keeps the builder simpler and aligns with typical usage.

I’ll push a small follow-up update shortly.

[Gosling-dude]

It looks like one Windows CI job (windows-latest, 8) failed while the rest passed. This may be transient. would you mind re-running that job when convenient?