fix(storage): Add telemetry tracing support for async stream Close()

[kalragauri]

This PR introduces OpenTelemetry tracing support for the newly introduced GCS Close() operation in the connection wrapper, ensuring end-to-end observability on connection half-close teardowns. This is a follow-up to #16112.

[gemini-code-assist]

Code Review

This pull request implements the Close method override in AsyncWriterConnectionTracing to enable OpenTelemetry tracing for close operations. It captures metadata such as message type, message ID, thread ID, and payload size, and logs a "gl-cpp.close" event. Additionally, corresponding unit tests (Close and CloseError) have been added to verify successful and failed close operations and their tracing events. I have no feedback to provide as there are no review comments.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.71%. Comparing base (77109ef) to head (960211a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #16118   +/-   ##
=======================================
  Coverage   92.71%   92.71%           
=======================================
  Files        2353     2353           
  Lines      219274   219314   +40     
=======================================
+ Hits       203303   203342   +39     
- Misses      15971    15972    +1     

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