This logic collects a list of known relays by testing every new connection.
It exists so we can dial /p2p-circuit/p2p/QmFoobar addresses (circuit addresses
that don't specify the relay). However, this kind of address is useless outside
of basic demos as a random relay is practically guaranteed to not be connected
to the target peer. Picking a random relay to connect to some peer is almost
_never_ the desired behavior.
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