Replace process-wide hash-slot mutexes with reference-counted locks keyed
by drive and path. Retain entries before waiting, acquire unique paths in
order, and reclaim entries only after all holders and waiters finish.
Add real storage API regressions for unrelated colliding objects and drives,
plus coverage for cancellation, multi-path order and waiter lifetimes.
Signed-off-by: Feng Ruohang <rh@vonng.com>
Feng Ruohang