DRAFT: interactive tx construction protocol

In a Bitcoin dev email thread, the topic of acceptable reuse in case of non-malicious failure after a valid PoDLE exchange was discussed. The default number of 3 for JoinMarket was considered reasonable. It was noted that limiting accepted node_ids to those previously seen in a node_announcement could help mitigate flooding. This is because node_announcement requires funds be allocated to a channel visible onchain. Therefore, if nodes send PoDLE gossip that they did not sign themselves, but are signed by some node that was node_announcemented before, we can identify those nodes that are spamming a lot of their own signed PoDLE gossip and rate-limit them. It was suggested that announced nodes are in the best position to inform others of such attempts and are the most likely to have such data. Set reconciliation for these also may be necessary at some point.