cksum: Flag handling differences (--debug and --algorithm)

[rsahwe]

--debug is missing and some other flags are handled differently or even inconsistently.

Choosing --algorithm sha2 is invalid and replaced by the more clear sha224, sha256, ...
but sha3 is not even listed in the help output and choosing it (or shake128 or shake256) gives the error message:
--bits required for SHA3 even though the GNU counterpart uses --length (inconsistently I know) and the --bits option doesn't even exist (even though there is code to support it such as uucore::features::checksum::create_sha3).

As far as I know these Issues were not reported / discussed before and the --bits flag being missing seems like an oversight.

(This causes gnu/tests/cksum/cksum to fail due to --debug failing and gnu/tests/cksum/cksum-raw failing due to the difference in algorithm handling)

[rsahwe]

Looking into it, it seems that the only problem (besides the --debug flag) is that there is no way to specify the type of sha3 hash. (Maybe a naming difference for the shake hashes?)

[cakebaker]

@rsahwe sha3 support is a recent feature of GNU cksum, it was added with v9.8. And we don't support it yet.