chore(o11y): remove beta api from observability classes

[blakeli0]

This PR remove @BetaApi from observability classes. @InternalApi annotations are also removed because they are either package private or need to be used externally.

[gemini-code-assist]

Code Review

This pull request promotes OpenTelemetryMetricsFactory to the public API and refactors its unit tests to use concrete objects instead of mocks. The review identifies a potential thread-safety issue with the clientLevelTracerContext field and suggests caution when removing API stability annotations. Additionally, the reviewer noted that the test refactoring removed a verification step for context merging, which should be restored to maintain adequate test coverage.

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sdk-platform-java/gax-java/gax/src/main/java/com/google/api/gax/tracing/OpenTelemetryMetricsFactory.java (41-42)

Removing @InternalApi and @BetaApi promotes this class to the public stable API. Avoid introducing breaking changes to public APIs, even if they have not been part of a public release. Additionally, the clientLevelTracerContext field is not volatile, which can lead to thread-safety issues if the factory is shared across threads. Please ensure the field is volatile or that access is properly synchronized.

References

1. Avoid introducing breaking changes to public APIs, even if they have not been part of a public release.

sdk-platform-java/gax-java/gax/src/test/java/com/google/api/gax/tracing/OpenTelemetryMetricsFactoryTest.java (82)

The test coverage has been weakened by removing the verify call. The current assertion only checks that the returned object is an instance of OpenTelemetryMetricsTracer, but it no longer verifies that the clientLevelTracerContext and methodLevelTracerContext are correctly merged. Please restore the verification logic to ensure the merging logic is correctly exercised.