Duplicate post-fork traces eliminated; OpenAI sentinel noise fixed

Bug Fixes

• tracing: This fix resolves an issue where traces buffered before os.fork() could be sent twice, once by the parent and once by the child.

• LLM Observability: Resolves an issue where the OpenAI integration recorded unset request parameters (OpenAI SDK's Omit/NotGiven sentinel values) as noise in LLM span metadata.

• profiling: Rare crashes that could happen post-fork in fork-based applications have been fixed.