Add KES key generation

[SebastienGllmt]

It's unclear what we need to do to get KES generation working well in our library.

There exists a Rust KES implementation by IOHK (https://github.com/input-output-hk/kes-mmm-sumed25519) but I'm not sure if it's compatible with the Haskell implementation of Cardano.

To quote IOHK on this matter:

Duncan Coutts

We are not using the Rust KES impl. We've had the one we are using audited, but we did want to compare to the rust one as a reference. We spent some time trying to compare the two impls but got to a bit of an impasse. There are two Rust impls, the "naive recursive" one and the "production" one. There are no Haskell bindings for the recursive one so it makes it hard to compare. It appears however that the recursive one at least would produce the same size output as we expect (and as expected from the paper).

Vincent Hanquez

There’s no difference of “algorithms” between the two rust versions above. Case in point, the naive version is used to KAT test the production version.