Document how to integrate with `IDisputeGame` for any type of proof

[pauldowman]

IDisputeGame is suitable for any type of proof, not just fault dispute games. It's even suitable for something that proves every block and posts proofs regularly. It may eventually be the basis for an aggregate dispute game which combines different dispute games together.

But it's not clear, especially because the name sounds like it's oriented toward fault proofs.

We need to document how to implement other types of proofs using IDisputeGame.

[ajsutton]

As part of this I suggest we create an example of a very different but simple style of dispute game. For example something that treats an output as valid if a signature is provided that attests to it (EAS style but dead simple) - maybe signing anchor state output ++ proposed output to simulate verifying from one agreed block to the new proposal. If that verification is encapsulated to a verify method it should be a really useful example of how to plug in different one-off verification systems like ZK sync.