fix use-after-free of a blackboard entry held by getAnyLocked

[aysha-afrah26]

Blackboard::getAnyLocked builds the returned AnyPtrLocked from a shared_ptr<Entry> that is a local variable, so the caller ends up holding a raw Any* and a raw std::mutex* into an entry that nothing keeps alive. unset() and clear() take storage_mutex_ but never entry_mutex, so erasing the key drops the last reference and destroys the entry while its mutex is still locked, which makes the next read through the pointer a heap-use-after-free and leaves ~LockedPtr unlocking a mutex that is already gone. The path I ran into it on is the Groot2 server thread, where ExportBlackboardToJSON calls getAnyLocked per key while an UnsetBlackboard action on the tick thread frees the entry underneath it; the test added here does the same sequence on a single thread and trips ASan on current master.

Giving LockedPtr an optional shared owner and passing it the shared_ptr<Entry> keeps the entry alive for exactly as long as the lock is held, which is what getInputStamped already does when it takes entry_mutex directly. Keeping it inside LockedPtr rather than at each call site means the guarantee holds for every user of the locked-pointer API instead of depending on each one to remember. One note for review: LockedPtr grows by one shared_ptr, and it only ever lives as a local scope guard so no class layout changes, but it is a size change in a public header.