Optimize execution gas usage

[mpetrun5]

Currently, we fetch and prove storage roots each proposal which costs per proposal when batched about 400k gas.
We need to avoid that cost and calculate that only once.

Implementation details

Calculate the necessary storage root before looping through the proposals and use that to verify the proposal with.
All the proposals should have the same source and security model.

Testing details

• unit tests

Acceptance Criteria

• cost when batching the next proposal should only include the cost to verify the proof against the precalculated storage root

[mpetrun5]

This should be tackled after the Axiom refactor that would change the executor logic to use storage roots directly instead of calculating them from the state root.