Remove TracerProvider.Tracer documentation about concurrent safety

[MrAlias]

The API does not contain, nor constrain, the implementation of the SDK. It is unfounded, and dangerous, to tell users of the trace API they can always call Tracer concurrently given it is SDK dependent.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.7%. Comparing base (90c75c4) to head (a47745a).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #7872   +/-   ##
=====================================
  Coverage   81.7%   81.7%           
=====================================
  Files        304     304           
  Lines      23245   23245           
=====================================
  Hits       19001   19001           
  Misses      3860    3860           
  Partials     384     384           

see 2 files with indirect coverage changes

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[Copilot]

Pull request overview

This PR removes the documentation stating that TracerProvider.Tracer is safe to call concurrently from the trace API interface. The reasoning is sound: the API interface does not constrain implementation details like thread safety, so documenting that all implementations must be concurrent-safe is misleading. Individual SDK implementations (like go.opentelemetry.io/otel/sdk/trace.TracerProvider) can and do document their own concurrency guarantees.

Changes:

• Removed two lines of documentation claiming concurrent safety from the TracerProvider.Tracer method in the trace API
• Added a changelog entry explaining the rationale and noting that the SDK implementation remains concurrent-safe

Reviewed changes

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

File	Description
trace/provider.go	Removed concurrent safety documentation from the Tracer method of the TracerProvider interface
CHANGELOG.md	Added changelog entry documenting this API documentation change

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[dashpole]

Lets wait for resolution of the spec issue before making changes here.

For context: open-telemetry/opentelemetry-specification#4867