Same message can be inserted into the Merkle tree hook multiple times

The same message can be inserted into the Merkle tree hook multiple times, as long as it is the latest dispatched message. We discussed if this behavior has been acknowledged and is acceptable on their side, because we were not aware of the way the off-chain components would interact with the Merkle tree hook contract.

The Hyperlane team has acknowledged that this is acceptable behavior and the off-chain component is responsible for handling this case correctly.