fix: use cancellable task for external scores sync

spawn_background_processor_task is reserved for the single LDK
background processor. The external scores sync was incorrectly
using it, which caused a debug_assert panic when Node::start()
later tried to spawn the actual background processor.

Switch to spawn_cancellable_background_task which matches the
pattern used by other periodic background tasks (RGS sync, peer
reconnection, broadcast queue).

Author: ovitrif

src/scoring.rs

@@ -25,7 +25,7 @@ pub fn setup_background_pathfinding_scores_sync(
 
 	let logger = Arc::clone(&logger);
 
-	runtime.spawn_background_processor_task(async move {
+	runtime.spawn_cancellable_background_task(async move {
 		let mut interval = tokio::time::interval(EXTERNAL_PATHFINDING_SCORES_SYNC_INTERVAL);
 		loop {
 			tokio::select! {