ZTS: Replace MD5 and SHA256 wit XXH128

[mcmilk]

For data integrity checks as done in ZTS, the verification for unintended data corruption with xxhash128 should be a lot faster and perfectly usable.

I removed the sysutils/coreutils dependency from FreeBSD and added xxhash everywhere.
The binaries md5, md5sum, sha256 and sha256sum are also not needed anymore.

How faster a whole functional testrun will be isn't known. But we can compare this runs of this PR with older ones.

Motivation and Context

Speedup ZTS a bit.

Description

How Has This Been Tested?

Timings for 2x zfs-tests.sh -vK -s 3GB -T rsend are like this:

system	xxhash128	md5 / sha256
qemu-x86 (almalinux8)	26m 47s	27m 50s
qemu-x86 (almalinux9)	28m 47s	29m 55s
qemu-x86 (centos-stream9)	29m 32s	29m 53s
qemu-x86 (debian11)	22m 56s	25m 1s
qemu-x86 (debian12)	24m 59s	27m 44s
qemu-x86 (fedora39)	29m 26s	30m 50s
qemu-x86 (fedora40)	27m 19s	29m 52s
qemu-x86 (freebsd13)	22m 43s	21m 56s
qemu-x86 (freebsd13r)	21m 33s	21m 59s
qemu-x86 (freebsd14)	19m 55s	21m 12s
qemu-x86 (freebsd14r)	20m 45s	23m 16s
qemu-x86 (ubuntu20)	22m 50s	25m 5s
qemu-x86 (ubuntu22)	27m 38s	29m 8s
qemu-x86 (ubuntu24)	30m 51s	31m 52s
Setup + Cleanup	32s	31s
Total	5h 56m 33s	6h 16m 4s

Links:

• old: https://github.com/mcmilk/zfs/actions/runs/11075750256 - Total duration: 34m 17s
• new: https://github.com/mcmilk/zfs/actions/runs/11075382905 - Total duration 31m 51s

It's not much, but it is just the rsend test, which uses checksums a lot.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.