WIP(wire): add v2 transport

[rustaceanrob]

Getting things rolling on BIP324 just to start a discussion. It will take some significant time for signet nodes to adopt this so it can actually be tested more thoroughly. In the meantime I am open for nits and nacks. I did a couple weird things like use a bunch of guard statements when trying the V2 connection instead of passing Result because I think the V2 connection should fail silently, as there is a lot that can go wrong and we should eagerly fall back to V1 instead of disconnecting. Writing V2 messages is not correct yet, as I need to add the correct message bytes.