Bypass channel monitor sync requests when no partition key given

NOTE(phlip9):
* Significantly reduces # of channel monitor persists during
  _transacion-only sync_.
* Backported from LDK master. See PR lightningdevkit#4544 for details.

Author: nicolft

lightning/src/chain/chainmonitor.rs

@@ -570,7 +570,7 @@ where
 				channel_id_bytes[2],
 				channel_id_bytes[3],
 			]);
-			channel_id_u32.wrapping_add(best_height.unwrap_or_default())
+			best_height.map(|height| channel_id_u32.wrapping_add(height))
 		};
 
 		let partition_factor = if channel_count < 15 {
@@ -580,12 +580,8 @@ where
 		};
 
 		let has_pending_claims = monitor_state.monitor.has_pending_claims();
-		if has_pending_claims || get_partition_key(channel_id) % partition_factor == 0 {
-			log_trace!(
-				logger,
-				"Syncing Channel Monitor for channel {}",
-				log_funding_info!(monitor)
-			);
+		if has_pending_claims || get_partition_key(channel_id).is_some_and(|key| key % partition_factor == 0) {
+			log_trace!(logger, "Syncing Channel Monitor");
 			// Even though we don't track monitor updates from chain-sync as pending, we still want
 			// updates per-channel to be well-ordered so that users don't see a
 			// `ChannelMonitorUpdate` after a channel persist for a channel with the same