Proof and verification key types across the stack

[codygunton]

Either I am missing the logic or there is none. Outside of the C++, we seem to variously use string[], Uint8Array and Buffer, and we have both "bytes" and "as fields" versions of various things. Someone should have a look at this and standardize. My dream would be a single source of truth in code, perhaps a msgpack schema for prover outputs, for instance, and a minimum number of copies/conversions between types.