Latency/peer disconnection may trigger us to mark as disabled
some of our channels. After some time, if channels are still
disabled we need to broadcast ChannelUpdate to inform other network
peers about the uselessness of these channels.
Because filter_block takes a and returns a list of s , we must add a lifetime to the ChainWatchInterface, which bubbles up in a lot of places. These places include adding a lifetime to the Node struct, which causes a lot of rearranging tests so that variables don't go out of scope before the Node that owns them does.
Adding this struct will allow us to remove the circular reference
between ChainListeners and the ChainWatchInterface, because it
separates out the responsibility of notifying listeners about new
blocks from the responsibility of storing and retrieving watched
transactions.
This includes the purpose of this PR, which is to remove the circular reference created by ChainListeners self-adding themselves to their ChainWatchInterface's `listeners` field.
