feat(spanner): add gax options for read/write transactions

[olavloite]

Adds methods for configuring GAX RequestOptions for the BeginTransaction and Commit RPCs of read/write transactions.

Updates #4972

[gemini-code-assist]

Code Review

This pull request enables configuring GAX request options (such as attempt timeouts, retry policies, and backoff policies) for both the BeginTransaction and Commit RPCs in read-write transactions. It introduces new builder methods on TransactionRunnerBuilder and ReadWriteTransactionBuilder to set these options, refactors option amendment logic, and adds comprehensive unit tests. The reviewer suggested an optimization in amend_gax_options to use std::mem::take instead of cloning GaxRequestOptions to avoid unnecessary allocations.

[codecov]

Codecov Report

❌ Patch coverage is 97.11340% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.88%. Comparing base (f075cec) to head (2247cf3).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/spanner/src/read_write_transaction.rs	96.61%	14 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #5787    +/-   ##
========================================
  Coverage   97.87%   97.88%            
========================================
  Files         226      226            
  Lines       56496    56938   +442     
========================================
+ Hits        55298    55731   +433     
- Misses       1198     1207     +9     

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[olavloite]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces configurable request options (begin_gax_options and commit_gax_options) for BeginTransaction and Commit RPCs in ReadWriteTransactionBuilder and ReadWriteTransaction, along with corresponding builder methods in TransactionRunnerBuilder. It also refactors amend_gax_options into a standalone helper function and adds extensive unit tests. Feedback highlights that TransactionBoundedRetryPolicy does not delegate on_throttle to its inner policy, which would cause custom throttling behaviors to be silently ignored, and suggests implementing delegation for on_throttle.

[olavloite]

/gemini review

[gemini-code-assist]

Code Review

This pull request adds configurable GAX request options (including timeouts, retry policies, and backoff policies) for the BeginTransaction and Commit RPCs in read-write transactions. It introduces several builder methods to TransactionRunnerBuilder and ReadWriteTransactionBuilder, refactors GAX options amendment, and adds comprehensive unit tests. Feedback is provided to improve the TransactionBoundedRetryPolicy's remaining_time implementation so that it respects any shorter timeout defined by the wrapped inner retry policy.

[olavloite]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces configurable GAX request options (such as attempt timeouts, retry policies, and backoff policies) for both the BeginTransaction and Commit RPCs within read-write transactions. It updates ReadWriteTransactionBuilder and TransactionRunnerBuilder with fluent builder methods to set these options, refactors the GAX options amendment logic to correctly respect and cap timeouts based on the transaction deadline, and adds comprehensive unit tests to verify the new behaviors. No review comments were provided, and the implementation is clean and idiomatic.