Expose router test utils as pub(crate)

Used in upcoming commit(s) to test onion message pathfinding

Author: valentinewallace

lightning/src/routing/mod.rs

@@ -12,3 +12,5 @@
 pub mod gossip;
 pub mod router;
 pub mod scoring;
+#[cfg(test)]
+pub(crate) mod test_utils;