Fix task store writes after parent directory removal

[baszalmstra]

Summary

• Prevent task store mutations from failing if the backing store parent directory is removed after initialization.

Changes

• Recreate the lock parent directory before acquiring a file lock.
• Recreate the store parent directory before writing the temporary file.
• Add a regression test that removes the parent directory between mutations.

Testing

• npm test
• npm run typecheck
• npm run lint