gh-111178: fix UBSan failures in `Modules/{blake2,md5,sha1,sha2,sha3}module.c` (GH-128248)

- fix UBSan failures in `blake2module.c`
- fix UBSan failures in `md5module.c`
- fix UBSan failures in `sha1module.c`
- fix UBSan failures in `sha2module.c`
- fix UBSan failures in `sha3module.c`

Cosmetics:

- suppress unused return values
- remove redundant casts in constructors
- suppress unused parameters in `{md5,sha*,blake2}module.c`