fix(retry): add Unauthenticated to retryable gRPC status codes to handle transient token expiration in storage control client

[meet2mky]

Description

This PR adds support for retrying gRPC Unauthenticated errors in the Storage Control Client to handle transient credential/token expirations. It also aligns the documentation and code comments across different retry mechanism.

Link to the issue in case of a bug fix.

b/517636259

Testing details

1. Manual - Yes
2. Unit tests - Yes
3. Integration tests - Part of pre-submit

Any backward incompatible change? If so, please explain.

NONE

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request improves the resilience of the Storage Control Client by enabling retries for gRPC Unauthenticated errors. This change ensures that transient token expiration issues are handled gracefully, reducing potential service disruptions. Additionally, the PR standardizes documentation and adds comprehensive test coverage to ensure the new retry behavior functions as expected.

Highlights

• Retry Logic Update: Added codes.Unauthenticated to the list of retryable gRPC status codes in the Storage Control Client to handle transient credential and token expiration issues.
• Documentation and Tracking: Updated code comments and TODOs with specific bug tracking references (b/518674297) to align documentation across retry mechanisms.
• Testing: Added a new unit test to verify that Unauthenticated errors are correctly identified as retryable by the control client.

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[gemini-code-assist]

Code Review

This pull request adds codes.Unauthenticated to the list of retryable gRPC status codes in both the storage control client wrapper and the integration test client options, accompanied by TODO comments referencing bug b/518674297. Additionally, it introduces a unit test to verify that unauthenticated errors are retryable and updates existing TODO comments in custom_retry.go to include the bug reference. There are no review comments, and I have no feedback to provide.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.72%. Comparing base (da692a3) to head (072a76f).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4746      +/-   ##
==========================================
+ Coverage   83.64%   83.72%   +0.07%     
==========================================
  Files         168      168              
  Lines       20775    20776       +1     
==========================================
+ Hits        17378    17395      +17     
+ Misses       2750     2736      -14     
+ Partials      647      645       -2     

Flag	Coverage Δ
unittests	83.72% <100.00%> (+0.07%)	⬆️

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