ACK

In the peerswap lnd and cln implementations we "ensure" that the receiver gets a message with brute force. We just resend the last message every `x` seconds until we receive a state update.

We might consider `ack` messages when we receive messages where the following state takes a while to proceed, e.g after `opening_tx_broadcasted`, we need to wait for a sufficiently deep confirmation.

This way we could still brute force send out the last message but could stop when we receive an `ack`.