Decide and define PublicKeys, PrivateKeys and Signatures serialization Strategy

[mxtartaglia-sl]

EcPublicKeys, EcPrivateKeys and EcSignatures need to be stored in state. Therefore need to be serialized.
The underlying objects (Pairings GroupElements and FieldElements) will know how to serialize themselves into byte arrays with the provided serialization mechanism from arkworks: https://github.com/arkworks-rs/algebra/blob/master/serialize/README.md
That byte array that is already canonically serialized needs to be appended with a value (the signature schema + some reserved bytes if decided) and returned in a way that will assure that it is produced deterministically.
This will not be exposed to the library's users. They don't need to know that protobuf will be used internally.

A suggestion instead of having a protobuf structure directly in the code is to produce the ByteString https://protobuf.dev/reference/java/api-docs/com/google/protobuf/ByteString instead.

We should go over and talk about alternatives. We should also understand the effect of introducing something other than direct serialization for consumers of the signature and the ledger when reading the blockade.

[mxtartaglia-sl]

@edward-swirldslabs summarized the definitions here: https://swirldslabs.slack.com/archives/C0718FR2FPB/p1726158751700539

Take aways:

• Serialization continue as planned, we will use the returned serialization from arkworks and append 1 byte to define the signature schema
• We need to converge the hashing mechanism to whatever can be used in S.C. possibly using KECCAK as hashing function + some encoding / mapping mechanism to the curve compatible with what can be produced in a s.c.
  This needs to be reviewed also by @rsinha . also cc: @AlfredoG87