Cache intermediate states of Power and Miner actors

[i-norden]

For proper execution of eth_call at "block" n we need to execute the call on top of the state that results from executing the messages in epoch n on top of the parent_state_root referenced from epoch n but before running the cron execution that brings us to the state under the parent_state_root referenced from epoch n+1.

In particular, it is the Power and Miner actors which exist in an intermediate state that does not exist at either n or n+1. If we cache the intermediate state for these actors, we should be able to use that in combination with the eventual states of the FEVM actors already captured at n+1 to perform eth_calls efficiently.