Override difficulty opcode

[Thegaram]

In l2geth we explicitly overridden the difficulty opcode so that it always returns 0:

https://github.com/scroll-tech/go-ethereum/blob/c27d82597bad7909695ad227f3043862f50e03da/core/vm/instructions.go#L523-L527

In scroll-revm we haven't added this, but it happens to work correctly because we always pass 0 difficulty. For clarity, and to avoid future issues, we should override this opcode.