Cardano.KESAgent.KES.Crypto

A stripped-down version of the OCert and Crypto types used in cardano-ledger. We only replicate what we need here, so as to avoid depending on cardano-ledger.

In order to keep things simple, we do not use the same CBOR serialization format for the OCert type; this would require using or replicating the CBORGroup functionality from cardano-ledger, which I feel would be too much to replicate here, and since the KES Agent protocols are not performance critical, the small overhead introduced by using the default CBOR serialization seems like an acceptable tradeoff.