[CacheService] Fix race conditions (MOB-23301)

Fix race conditions in the cache service when multiple extensions use the same cache. This issue doesn't occur now because each extension uses a separate cache.

Start by locating the CacheService implementation and tracing how multiple extensions access the same cache. Reproduce or reason about concurrent cache use, then identify the synchronization behavior needed so shared-cache operations are race-free. Done means concurrent extensions can safely use one cache without inconsistent results.

Written by the indexing model from the issue text.