feat: move state/receipt building to new method

Moves transaction processing logic of build_pending_state to a new
struct. Also separates out reusing a cached execution from executing
using the EVM.

This also removes block_hash from receipts and transactions which
matches the spec and removes the need for calculating a useless block
hash for every flashblock.

The next step is to move the for loop into this struct which will
return an iterator of results.

Using this, we'll be able to prewarm accessed addresses using FALs
and eventually process transactions in parallel. Moving execution to a
new struct allows us to implement a trait for building flashblocks and
switch out different implementations (prewarming, parallel,
sequential).

Author: meyer9