chore(spanner): wire location-aware routing into unary RPCs

[olavloite]

• Wire LocationRouter into unary database RPCs (begin_transaction, commit, rollback, execute_sql, execute_batch_dml, partition_read, partition_query).
• Add routing key extraction for PartitionReadRequest and PartitionQueryRequest.
• Track and enforce transaction server affinity for read-write transactions (including inline begin and commit/rollback lifecycle clearing).
• Ingest inline CacheUpdate from unary responses (CommitResponse, Transaction, ResultSet, ExecuteBatchDmlResponse).

[gemini-code-assist]

Code Review

This pull request implements location-aware routing for unary database RPCs (such as commit, rollback, execute_sql, and begin_transaction) in the Spanner client. It refactors routing resolution using a unified RoutingContext and introduces pre-route and post-route hooks to manage transaction affinity. Additionally, comprehensive mock tests are added to verify routing behaviors. The feedback suggests removing a redundant check for an empty or all KeySet in extract_proto_read_key_set_routing_key, as this is already handled internally by extract_key_from_proto_key_set.

[codecov]

Codecov Report

❌ Patch coverage is 98.98785% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.53%. Comparing base (80b3370) to head (06f7279).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/spanner/src/database_client.rs	98.71%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6562      +/-   ##
==========================================
+ Coverage   96.51%   96.53%   +0.01%     
==========================================
  Files         304      304              
  Lines       87943    88397     +454     
==========================================
+ Hits        84875    85330     +455     
+ Misses       3068     3067       -1     

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[olavloite]

/gemini review

[gemini-code-assist]

Code Review

This pull request implements location-aware routing for Spanner RPCs, including transaction affinity tracking for read-write transactions and support for partition read and query operations. It introduces pre-route and post-route hooks to the define_db_rpc macro to manage routing context and transaction affinity, along with comprehensive tests to verify the new logic. The reviewer suggested using the 'let Some(...) else' pattern in the pre_route methods to simplify early returns, which improves code readability and aligns with the repository's style guide.

[olavloite]

/gemini review

[gemini-code-assist]

Code Review

This pull request implements location-aware routing and transaction affinity tracking for unary database RPCs (such as begin_transaction, commit, execute_sql, execute_batch_dml, rollback, partition_query, and partition_read) in the Spanner client. It refactors the RPC macro definitions to support pre-routing and post-routing hooks, introduces a structured RoutingContext to manage routing decisions, and adds comprehensive unit and mock integration tests to validate the routing logic and affinity lifecycle. I have no feedback to provide as there are no review comments to assess.