chore(spanner): add key_recipe_cache

[olavloite]

Adds a cache for KeyRecipe.

[gemini-code-assist]

Code Review

This pull request introduces KeyRecipeCache, a thread-safe, concurrent cache for Spanner key recipes, separated by target type (tables, indexes, and queries) to enable zero-allocation lookups. The review feedback focuses on optimizing lock hold times and reducing lock contention within the cache. Specifically, it is recommended to perform deallocations of overwritten or cleared cache entries outside of the write lock by using std::mem::take and explicitly dropping the lock guard.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.25%. Comparing base (35b9590) to head (f88bee9).
⚠️ Report is 7 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #6280    +/-   ##
========================================
  Coverage   96.24%   96.25%            
========================================
  Files         280      281     +1     
  Lines       72146    72299   +153     
========================================
+ Hits        69440    69593   +153     
  Misses       2706     2706            

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[olavloite]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces KeyRecipeCache, a thread-safe, concurrent cache for Spanner key recipes (tables, indexes, and queries) backed by an RwLock over separate hash maps, along with comprehensive unit tests. The review feedback suggests refactoring the cache implementation by importing RwLockReadGuard and RwLockWriteGuard and introducing private helper methods read_store and write_store to centralize lock acquisition and error handling, which reduces code duplication across getter and setter methods.

[olavloite]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a thread-safe KeyRecipeCache to store table, index, and query key recipes, enabling local binary routing key encoding. The cache is backed by an RwLock over separate hash maps to support concurrent, non-blocking reads, and includes comprehensive unit tests. The review feedback suggests renaming the getter methods (get_table_recipe, get_index_recipe, and get_query_recipe) to omit the get_ prefix, in accordance with the repository's style guide and idiomatic Rust conventions.