Makes clear the distinction between Finalize and FinalizedAndAssemble:

- In Finalize function, a series of state operations are applied according to consensus rules. The statedb is mutated and the root hash can be checked and compared afterwards.

This function should be used in block processing(receive afrom network and apply it locally) but not block generation.

- In FinalizeAndAssemble function, after applying state mutations, the block is also to be assembled with the latest
  state root computed, updating the header. 

 This function should be used in block generation only.