the while loop in `suggest_node_channel_open()` of lnrater would not
break if there are no "good" peers available available. As a result the gui
blocks and electrum has to be killed. This can happen for example on
signet.
This removes the tested pk from the list of candidates so each candidate
gets tested only once.
`suggest_node_channel_open()` did suggest peers with onion hostname,
even if the caller has no proxy enabled. This causes channel openings in
the gui to sometimes just not work and show a `CancelledError()` becaues
it wasn't able to connect to the peer.
Now only clearnet peers will get recommended, as these will always work.
Introduces LNRater, which analyzes the Lightning Network graph for
potential nodes to connect to by taking into account channel capacities,
channel open times and fee policies. A score is constructed to assign a
scalar to each node, which is then used to perform a weighted random
sampling of the nodes.
