Enhancement: Show progress bar for `restic stats`

Previously, running `restic stats` would only give progress updates for loading the index.
Now it displays progress for how many snapshots, files, and blobs were processed so far.
This lets users better understand if the command is working as expected or where it is hanging.

https://github.com/restic/restic/issues/5689
https://github.com/restic/restic/pull/5705