Version all on-chain state

[benluelo]

All light clients and apps should use some form of versioning for their state, to ensure backwards compatability. ucs03-zkgm already has this with it's instructions, but the lightclients still need this. Since we use bincode for our state codec, we should use something like this:

#[non_exhaustive]
enum ClientState {
    V1(ClientStateV1),
    V2(ClientStateV2),
}

to allow for adding new state versions while still being able to decode old versions. This will remove the majority of the need for complex state migrations of light client state.