Ensure graceful degradation on network drives (SMB/NFS)

[Rakshat28]

Running bdstorage against a NAS (Network Attached Storage) mounted via SMB or NFS is a massive edge case. Network protocols often drop or reject low-level Linux system calls like ioctl(fiemap) or BTRFS_IOC_CLONE.

Acceptance Criteria:

• Test the scan and dedupe pipelines on a locally hosted SMB or NFS share.
• Ensure that if fiemap ioctls fail over the network, the engine gracefully falls back to the full-file hash instead of panicking.
• Ensure clear error messages are surfaced to the user regarding the inability to reflink over a network mount.