Fast_copy new release with new features

fast-copy v3.12.3

A large consolidated release covering everything since the 3.7 line: new
transports and dedup engines, full file and directory metadata preservation,
and a substantial correctness and security hardening pass.

New features

• SMB/CIFS (smb://, UNC): native transport to and from Windows shares and Azure Files.
• --index-existing: reflink-dedup a copy against files that already exist at the destination.
• --dedup-existing: in-place reflink merge of duplicate files already on disk.
• ReFS block cloning on Windows (real copy-on-write clones).
• Metadata preservation for directories as well as files (mode/owner/times/xattr/acl, incl. setuid/setgid and the remote-to-local pull path).
• GUI: SMB credential management and an in-app self-update flow.

Improvements

• --preserve acl is ~3.5-4x faster (xattr fast-path).
• Much faster large dedup trees via HDD-aware hashing and a persistent hash cache.
• Full extent dedup for large files (accurate reclaimed-space reporting).
• Live progress everywhere: per-phase timing, files/sec, link/verify/index progress.
• Verify explains the real cause of a failure.
• Batched SQLite commits; AES-GCM credential encryption (no plaintext).

Bug fixes

• FAT32/removable destinations copy correctly; an incomplete verify now fails the run.
• Cross-mount source is warned and skipped instead of crashing.
• --index-existing edge cases (non-UTF-8 names, hash-algorithm mismatch, empty-file linking).
• --ssh-no-sftp directory nesting.
• Security: setuid/setgid privesc hardening, O_NOFOLLOW TOCTOU mitigation, updated crypto deps.