Notify scorer of failing payment path and channel

Upon receiving a PaymentPathFailed event, the failing payment may be
retried on a different path. To avoid using the channel responsible for
the failure, a scorer should be notified of the failure before being
used to find a new route.

Add a payment_path_failed method to routing::Score and call it in
InvoicePayer's event handler. Introduce a LockableScore parameterization
to InvoicePayer so the scorer is locked only once before calling
find_route.

Author: jkczyz

lightning-background-processor/src/lib.rs

@@ -311,6 +311,7 @@ mod tests {
 	use lightning::ln::features::InitFeatures;
 	use lightning::ln::msgs::{ChannelMessageHandler, Init};
 	use lightning::ln::peer_handler::{PeerManager, MessageHandler, SocketDescriptor, IgnoringMessageHandler};
+	use lightning::routing::scorer::Scorer;
 	use lightning::routing::network_graph::{NetworkGraph, NetGraphMsgHandler};
 	use lightning::util::config::UserConfig;
 	use lightning::util::events::{Event, MessageSendEventsProvider, MessageSendEvent};