feat(o11y): generate updated clients with LRO span creation

[haphungw]

sidekick was updated to create and enter a T2 span with the literal method name before calling the poller factories. This ensures that the span name conforms to the design spec (e.g., client::Workflows::create_workflow.Wait).

All new tracing code is gated behind the google_cloud_unstable_tracing flag.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.71%. Comparing base (44840ac) to head (6fdb25f).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5629      +/-   ##
==========================================
- Coverage   97.76%   97.71%   -0.05%     
==========================================
  Files         221      221              
  Lines       51115    51175      +60     
==========================================
+ Hits        49971    50007      +36     
- Misses       1144     1168      +24     

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[gemini-code-assist]

Code Review

This pull request updates generated code across multiple services to include tracing spans for long-running operation pollers and transitions to a more flexible poller initialization method. It also improves documentation examples for resource identifiers. Feedback identifies that the removal of specific link definitions in doc comments breaks existing references, suggesting a systematic generator issue. Additionally, it is recommended to use more robust tracing patterns like in_scope or .instrument instead of span.enter() to avoid potential issues in asynchronous contexts.