op-challenger: Adjust honest actor behaviour to counter freeloaders.

[ajsutton]

Description

Built on https://github.com/ethereum-optimism/optimism/pull/9637 this adjusts the honest actor behaviour to get all tests passing.

The rules are now simple, for each claim in the game:

1. If the claim is one the honest actor would make, do not counter it (no self-countering)
2. If the ancestor of the claim with the highest trace index, less than the position of the counter claim is invalid, do not counter it (avoid poisoned prestates)

Otherwise, counter the claim, attacking or defending based on whether the claim value is correct or not.

Note the existing step unit tests are failing - I have changed the AttemptStep function to have the same semantics as NextMove for consistency so the tests will need updating, but I can't work out why those tests were expecting to not call step in that situation - seems wrong to me....

Metadata

• https://github.com/ethereum-optimism/client-pod/issues/103