Fix NFS cache lock timeouts and add stale lock cleanup

- Reduce lock timeout from 1 hour to 2 minutes (NFS writes take ~10s)
- Add stale lock detection and automatic cleanup (>10 min old)
- Add timing instrumentation for lock acquisition and tar operations
- Log throughput for debugging (MB/s for tar create/extract)
- Clean up stale locks before attempting new lock acquisition
- Add lock holder info file for debugging stuck locks