Add unsquashfs and stop SquashFS tools failing on xattrs

Install Ubuntu's squashfs-tools so the stock unsquashfs/mksquashfs exist
next to sasquatch. As the non-root container user, unsquashfs and
sasquatch can't restore security.* xattrs and exit 2 although every file
was extracted; wrap them to pass -no-xattrs unless an xattr option is
given.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/squashfs-no-xattrs.sh

@@ -0,0 +1,16 @@
+#!/bin/sh
+# Installed in the image as /usr/local/bin/{unsquashfs,sasquatch,sasquatch-v4be}
+# (symlinks to this script), in front of the real tools in /usr/bin.
+#
+# As the unprivileged container user these tools can't restore security.*
+# xattrs (SELinux labels, file capabilities) that firmware images often
+# carry: they extract every file but print "not superuser" errors and exit 2,
+# which reads as a failed extraction. Pass -no-xattrs unless the caller
+# already chose an xattr option (-xattrs, -user-xattrs, -xattrs-include, ...).
+tool="/usr/bin/$(basename "$0")"
+for arg in "$@"; do
+    case "$arg" in
+        -*xattrs*) exec "$tool" "$@" ;;
+    esac
+done
+exec "$tool" -no-xattrs "$@"