This PR updates the BAL structure definition to the latest the spec,
- Balance has been changed from [16]byte to uint256
- Storage key and value has been changed from [32]byte to uint256
- BlockAccessList has been changed from a struct to a slice of
AccountChanges
- TxIndex has been changed from uint16 to uint32
This PR refactors the encoding rules for `AccessListsPacket` in the wire
protocol. Specifically:
- The response is now encoded as a list of `rlp.RawValue`
- `rlp.EmptyString` is used as a placeholder for unavailable BAL objects