Re-investigate possible support for Argon2id

[brycx]

I was recently asked whether Orion had plans to support Argon2id. We've never been opposed to this variant in general, but the last time this was investigated was when Argon2i was being implemented.

At that time, there seemed to be no easy way to support the parallelism of Argon2d, without either implementing the threading-logic ourselves or pulling in dependencies with a lot of unsafe code.

I think it would be worthwhile to re-investigate this, to see if anything has changed in terms of how parallelism could be supported.