Emit SpliceFailed event when channels close with pending splice actions

Users need to be notified when splice operations are cancelled due to channel
closure, regardless of the splice phase. Previously, splice operations that
were scheduled but not yet in active negotiation were silently lost during
channel shutdown, leaving users unaware of the failed splice attempt.

Now emits Event::SpliceFailed when a channel shuts down with a pending
QuiescentAction::Splice, ensuring comprehensive splice failure reporting
across all phases of the splice lifecycle.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: jkczyz

lightning/src/ln/channel.rs

@@ -6877,6 +6877,22 @@ where
 					contributed_inputs: Vec::new(),
 					contributed_outputs: Vec::new(),
 				}
+			})
+			.or_else(|| {
+				// Also check for pending quiescent action that is a splice
+				if let Some(QuiescentAction::Splice(_)) = self.quiescent_action.take() {
+					Some(SpliceFundingFailed {
+						channel_id: self.context.channel_id,
+						counterparty_node_id: self.context.counterparty_node_id,
+						user_channel_id: self.context.user_id,
+						funding_txo: None,
+						channel_type: None,
+						contributed_inputs: Vec::new(),
+						contributed_outputs: Vec::new(),
+					})
+				} else {
+					None
+				}
 			});
 
 		let mut shutdown_result = self.context.force_shutdown(&self.funding, closure_reason);