Zilliqa API should query state from the finalized block rather than the latest block

[JamesHinshelwood]

The ZQ1 API made the guarantee that data returned from the Zilliqa API would be consistent. However, ZQ2 does not have single-block finality any more so in order to maintain this guarantee we should return state from the finalized block instead of the latest block. We should also not (yet) return a response for transaction receipts, etc. if they are mined after the finalized block.