feat(o11y): propagate LRO destination ID to child spans

[haphungw]

Introduce stateful propagation of the LRO destination ID (resource ID/operation name) across LRO polling attempts inside google-cloud-lro.

[gemini-code-assist]

Code Review

This pull request introduces tracking and recording of the destination ID for long-running operations (LRO) within LroRecorder by adding a thread-safe destination_id field, implementing helper methods, updating the polling attributes macro, and adding corresponding tests. The review feedback recommends simplifying the implementation by replacing std::sync::RwLock with std::sync::Mutex for the destination_id field, which aligns with the repository's style guide to avoid unnecessary complexity.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.88%. Comparing base (094bf6d) to head (c9a339a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5871      +/-   ##
==========================================
- Coverage   97.89%   97.88%   -0.01%     
==========================================
  Files         227      227              
  Lines       57995    57995              
==========================================
- Hits        56774    56770       -4     
- Misses       1221     1225       +4     

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