squashfs-tools from Buster (1:4.3-12) is much slower than 1:4.3-8.0tails1

Compressing the SquashFS on lizard jumped from 20 min to 38 min since we upgraded from 1:4.3-8.0tails1.

Feature Branch: bugfix/16637-faster-mksquashfs

Original created by @intrigeri on 16637 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information