Fix Imp fixup for Plutus scripts in subtransactions

At the moment, Imp framework doesn't support submitting transactions with subtransactions that have Plutus V4 scripts - unless the witnesses and redeemers are added manually.
We should update the dijkstra fixup that allows us to easily submit these.

Start by locating the Dijkstra fixup used by the Imp framework and inspect how it handles subtransactions with Plutus V4 scripts. Reproduce the transaction-submission case described in the issue, then verify that witnesses and redeemers no longer need to be added manually.

Written by the indexing model from the issue text.