offchain: adjust code to avoid some clippy warnings

[marcelstanley]

I have no strong opinions about the changes made at 2657bd5f to the State sub-types to meet new_ret_no_self. We can easily dispense with it and move forward if you prefer.

As stated at https://github.com/cartesi/rollups-node/issues/37#issue-1824961694, we're still going to miss changes to meet module_inception. Also, as mentioned at https://github.com/cartesi/rollups-node/issues/37#issuecomment-1654524395, I see no reason to fix too_many_arguments warning.

Closes cartesi/rollups-node#37

[marcelstanley]

Obsoleted by cartesi/rollups-node#47