feat(o11y): extract error details and type for Discovery LROs

[haphungw]

Now that the generator template and the LRO macro are fixed, we implement the actual telemetry error mapping for Compute Engine LROs and adds integration test assertions.

[gemini-code-assist]

Code Review

This pull request implements the error method for Operation in the generated Compute v1 client, integrates the record_discovery_polling_result! macro for tracing, and adds integration tests to verify LRO error tracing. Feedback on the changes highlights a logical bug in operation.rs where an HTTP status of 200 is mapped to Code::Unknown instead of Code::Ok, causing successful operations to be incorrectly treated as errors. Additionally, because operation.rs is a generated file, this fix must be applied to the generator template rather than the file directly.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.70%. Comparing base (74a8c5b) to head (21c498e).

Files with missing lines	Patch %	Lines
src/lro/src/internal/discovery.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5955   +/-   ##
=======================================
  Coverage   97.70%   97.70%           
=======================================
  Files         242      242           
  Lines       60891    60894    +3     
=======================================
+ Hits        59494    59498    +4     
+ Misses       1397     1396    -1     

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