refactor(Hash): store raw digest bytes in arrays

[selfisekai]

BREAKING CHANGE: new type signature of Hash, digest lengths are now validated

Fixes: #5

[zkat]

This is a pretty big, API-visible breaking change. While the refactor does seem nicer, do you have benchmark numbers on what difference they might make? The difference would need to be noticeable in order to justify this, imo.

[selfisekai]

No, my focus was on correctness. Seems to be less than statistical error on a quick check.

Added new APIs for convenience. I think all API breakages have an easy migration path now:

• Hash { algorithm, digest } -> Hash::from_algorithm_digest_str(algorithm, digest)
• hash.algorithm -> hash.algorithm()
• hash.digest -> hash.digest_base64()

[zkat]

I'm gonna sit on this for a bit. ssri has been fairly stable for a while and if I'm gonna put out a breaking change, I'd like to have more substantial stuff bundled with it.