Research if we can restrict index to `U64` block spec in `eth_getTransactionByBlockHashAndIndex`

[agostbiro]

We currently accept U256 in eth_getTransactionByBlockNumberAndIndex in order to match Hardhat returning null for out of bound indexes. We need to determine if we could make it an error to specify a larger index than a U64.

Definition of done

Determine if Geth returns null or an error for indices larger than U64 in eth_getTransactionByBlockNumberAndIndex and create follow up task to implement if we can restrict indices to U64.