[local storage] Remove IPC lock file after releasing the lock

[Sanjays2402]

Closes #1975

Description

fasteners.InterProcessLock creates its lock file but never removes it, and
LockLocalStorage.__exit__ did not remove it either. The file name is a sha256
of the locked path, so one file was left behind in the temp directory for every
distinct path ever locked -- a long running process writing many objects can
exhaust inodes. The lock file is now removed after the IPC lock is released.

Status

done, ready for review

Checklist (tick everything that applies)

• Code linting (required, can be done after the PR checks)
• Documentation
• Tests
• ICLA (required for bigger changes)

[micafer]

Removing the lock file immediately after releasing InterProcessLock introduces a race which can break mutual exclusion.

For example, process B may acquire the existing file lock immediately after process A releases it. A can then unlink the path, and process C can create and lock a new file at the same path. B and C would consequently hold locks on different inodes and could both enter the critical section.

The new test only verifies that the file is removed in a non-concurrent scenario, so it does not cover this race or verify that mutual exclusion is preserved.

I don't think the lock file can safely be removed as part of exit. We likely need a different bounded-lock or out-of-band cleanup strategy.