Chore/block signature message type

[jferrant]

Closes https://github.com/stacks-network/stacks-core/issues/4784

I made the process_event logic take a generic type which implements StacksMessageCodec to enable having different message types for v1 and v2 without borking up code in each respective path. I also implemented a helper function for creating a v1 signer. This same logic can easily be added for a v0 signer which wraps the super confusing looking RunningSigner struct.