Incorporate suggestions of Larry Doolittle.

SquashFS metadata & compression

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When compressing SquashFS images, metadata and compression can make the output unreproducible.

When compressing SquashFS images, metadata and compression can make the output

unreproducible.

Using a version of `mksquashfs` that contains the following patches has been sufficient

to make some system images reproducible:

When building SquashFS images, older versions of the tools sometimes yielded

unreproducible results. A good `mksquashfs` will:

 - honoring `$SOURCE_DATE_EPOCH` for various timestamps:

   <https://github.com/squashfskit/squashfskit/commit/0ab12a8585373be2de5129e14d979c62e7a90d82>

 - clamping content timestamps to `$SOURCE_DATE_EPOCH`:

   <https://github.com/squashfskit/squashfskit/commit/32a07d4156a281084c90a4b78affc8b0b32a26fc>

 - remove `frag_deflator_thread`:

   <https://github.com/squashfskit/squashfskit/commit/afc0c76a170bd17cbd29bbec6ae6d2227e398570>

* Honor $SOURCE_DATE_EPOCH for various timestamps

* 'Clamp' content timestamps to $SOURCE_DATE_EPOCH

* Not reorder fragments based on multithreading conditions

[squashfs-tools](https://github.com/plougher/squashfs-tools) 4.5.1 (in Debian

*bookworm*) is should work here, having absorbed important features from

[squashfskit](https://github.com/squashfskit/squashfskit).

Root filesystem content

=======================