RPC08 - starknet_getMessagesStatus

[rianhughes]

starknet_getMessagesStatus

https://docs.starknet.io/architecture-and-concepts/network-architecture/messaging-mechanism/#l1-l2-messages

see: eqlabs/pathfinder#2182

Solution:

1. Listen to LogMessageToL2 logs from the core contract on L1. Compute the associated message hash, and store the eth transaction hash. Note that a single L1 transaction can induce multiple messages.
   Populate db with: map[eth transaction hash][]message hash
2. When syncing L2. Compute the message hash for l1 handler transactions.
   Populate db with: map[message hash]l1_handler_transaction_hash

Overall this allows us to map eth_txn_hash to l1_handler_txn_hash, which we can then serve over RPC.

[rianhughes]

L1 message (not transaction) hash is computed as

keccak256(
    abi.encodePacked(
        uint256(FromAddress),
        ToAddress,
        Nonce,
        Selector,
        Payload.length,
        Payload
    )
);