What

Add `GUARDED_BY(_mutex)` to the member fields in `LogicalSessionCacheImpl` accessed without the mutex. Add `REQUIRES(_mutex)` to private helpers that read or write them.

Files: `logical_session_cache_impl.cpp` (lines 344, 346).

Resolves: SERVER-109412, SERVER-112002

Why

Session cache state is accessed from multiple threads under executor scheduling. Because Coverity cannot be run locally, `GUARDED_BY` annotations are the practical way to confirm the fix is complete and to prevent these fields from being accessed without the lock in the future.