Fix race when publishing deserialised KV maps

[achamayou]

Summary

• hold the Store map-set lock while deserialised transactions validate and publish new dynamic maps
• add a concurrent regression that applies serialised map creations while readers look up maps

Background

fill_maps() discovers missing maps while holding maps_lock, but releases that lock before commit_deserialised() calls apply_changes(). The latter publishes each map through add_dynamic_map(), mutating Store::maps concurrently with readers in get_map_internal().

The new regression reproduces 4 TSAN warnings before the fix, with the same get_map_internal()/add_dynamic_map() access pair seen while investigating #8002. The race predates that PR.

Testing

• Debug kv_test: passed
• TSAN kv_test: passed with no sanitizer warnings
• C++ formatting, includes, copyright, and ASCII checks: passed

[Copilot]

Pull request overview

This PR fixes a TSAN-detected data race in CCF’s KV Store by ensuring the map-set (Store::maps) is not mutated concurrently with map lookups when committing deserialised transactions that publish newly created dynamic maps.

Changes:

• Hold maps_lock during Store::commit_deserialised() when new_maps is non-empty, preventing concurrent add_dynamic_map() mutations of Store::maps while readers call get_map_internal().
• Add a concurrent regression test that applies serialised dynamic-map creations while multiple reader threads repeatedly look up a (missing) map name to exercise the previously-racy access pattern under TSAN.

Custom instructions used:

• .github/copilot-instructions.md
• .github/instructions/reviewing.instructions.md

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/kv/store.h	Conditionally acquires maps_lock across apply_changes() during deserialised commits when dynamic maps may be published.
src/kv/test/kv_dynamic_tables.cpp	Adds a TSAN-focused concurrency regression test covering concurrent map publication vs. map lookup.