hashsum: should refuse to run with contradictory bitlengths

[BenWiederhake]

Doesn't work as hashsum

$ cargo run -q hashsum --sha3-512 --bits 256 README.md
5bde479913538c7f932e8521719ab5ffea4e7b12b68905a9c147341090d8f738165f5a30fc5d2c05a320d500dcf912e40c77f78ae3236a9118a1be2e5fe35340  README.md

Doesn't work as sha3sum

Tightly related, perhaps the same bug:

$ cargo build -p uu_hashsum
$ ln -s target/debug/hashsum sha3sum
$ ./sha3sum README.md 
./sha3sum: --bits required for SHA3
[$? = 1]
$ ./sha3sum --bits 256 README.md 
./sha3sum: --bits required for SHA3
[$? = 1]
$ ./sha3sum --bits 256 --bits 256 README.md 
./sha3sum: --bits required for SHA3
[$? = 1]

Doesn't work as sha3-384sum

$ cargo build -p uu_hashsum
$ ln -s target/debug/hashsum sha3-384sum
$ ./sha3-384sum README.md 
./sha3-384sum: --bits required for SHA3
[$? = 1]
$ ./sha3-384sum --bits 256 README.md 
error: unexpected argument '--bits' found

  tip: to pass '--bits' as a value, use '-- --bits'

Usage: ./sha3-384sum [OPTIONS] [FILE]...

For more information, try '--help'.
[$? = 1]

Found while reading #6431, still applies to current main.