fix(bigquery): enforce idempotency requirements in retry policy

[alvarowolfx]

Add check for duplicated job error and increase test coverage for idempotency settings.

Towards #6717 #6218

[gemini-code-assist]

Code Review

This pull request updates the BigQuery query retry policy to respect idempotency. Specifically, in RetryableErrors::on_error, if the request state is not idempotent, the retry policy now returns a permanent error. Additionally, a helper function is_duplicate_job_error is introduced to identify duplicate job errors (HTTP 409 or AlreadyExists), and comprehensive unit tests are added to verify these behaviors. I have no feedback to provide.

[alvarowolfx]

Split from #6780

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.03%. Comparing base (c5563c1) to head (4a04cf3).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6798   +/-   ##
=======================================
  Coverage   97.02%   97.03%           
=======================================
  Files         326      326           
  Lines      107430   107511   +81     
=======================================
+ Hits       104238   104322   +84     
+ Misses       3192     3189    -3     

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