Feature Request: Support archive-based backup format (tar.gz/zip) for NTFS compatibility

Hi Timeshift team,

I would like to request a new feature: supporting compressed archive formats (e.g., tar.gz, tar.xz, zip) for backups, instead of only relying on rsync or BTRFS snapshots.
The Problem

Currently, Timeshift requires an ext4-formatted partition (or BTRFS) to store backups. This creates a major inconvenience for users who:

Dual-boot Windows + Linux
Only have NTFS-formatted external drives available
Don't want to (or can't) repartition their drives to create a new ext4 partition just for backups

As a result, I currently have to reformat or create a new ext4 partition on my NTFS drive just to use Timeshift, which is very inconvenient.
The Solution

If Timeshift could save backups as compressed archive files (like .tar.gz, .tar.xz, or .zip), users could:

Store backups on any file system — NTFS, FAT32, exFAT, ext4, etc.
No need to create a dedicated ext4 partition
Still benefit from compression to save disk space
Easily browse or extract individual files if needed

This is a very common request from dual-boot users, who often only have NTFS drives available and lack extra ext4 partitions.
Summary

RSYNC: Requires ext4, does NOT work on NTFS, NOT compressed
BTRFS: Requires ext4, does NOT work on NTFS, NOT compressed
tar.gz (proposed): Does NOT require ext4, WORKS on NTFS, compressed

I believe this feature would greatly improve Timeshift's usability for dual-boot and multi-OS users.

Thank you for your great work on Timeshift!

— A user from China

Start by reviewing Timeshift's existing rsync and BTRFS snapshot and restore paths. Trace how snapshot storage and restoration currently depend on the filesystem, then determine the scope needed for archive-based backups. Done should include creating and restoring compressed archives on NTFS and other supported filesystems, with the requested archive formats clarified.