New sync command

This command compares the content of an archive, or one of its subfolders, with a filesystem.
It is generally recommended to use absolute paths rather than relative ones.
It essentially serves two purposes:

1. Test or verification: After performing an archive with the a command, a "heavy" verification can be done with the sync command (use -quick to skip hash checking and only compare sizes, or -ssd to enable multithreading on non-rotational disks).
2. Estimate data: Estimate how much data would be archived if an update for a new version were performed.
   It differs from the v (verify) command because it also shows new files not present in the archive and those that are missing.

Multithread support for the t (test) command

It is now possible to use all cores in the second phase (CRC-32 reconstruction).
This has no significant impact if there are few archived files (e.g., a single virtual disk image), but it can reduce processing time by up to ten times in optimal cases (e.g., millions of small files, such as on a file server).
Note: This feature is not extensively tested.

Default progress is now displayed at one-second intervals

Instead of updating based on ETA changes, this reduces console impact for very large jobs.

Attempt (harder) to restore text color when pressing Ctrl+C

Using -stat adds |STAT| to output lines

This facilitates the removal of sensitive information for privacy purposes (e.g., using grep, awk, etc.) when sending logs via email.

Renamed the key file for the sftp command to -ssh

Further refactoring, likely introducing new bugs

Various minor internal improvements