fix: clear pending pings to avoid promise leaks on connection close/suspend

- Add cancel() method to RttCommand to fail promise on connection close
- Add dequeueAll() method to ConcurrentQueue for batch cleanup
- Call clearPendingPings() in close(), suspend(), and disconnect() methods
- Prevents 'leaking promise' crash when connection is closed while pings are pending

Sources/Nats/NatsConnection.swift

@@ -712,6 +712,7 @@ class ConnectionHandler: ChannelInboundHandler {
         guard let eventLoop = self.channel?.eventLoop else {
             self.state.withLockedValue { $0 = .closed }
             self.pingTask?.cancel()
+            clearPendingPings()  // Clear pending pings to avoid promise leaks
             self.fire(.closed)
             return
         }
@@ -720,6 +721,7 @@ class ConnectionHandler: ChannelInboundHandler {
         eventLoop.execute {
             self.state.withLockedValue { $0 = .closed }
             self.pingTask?.cancel()
+            self.clearPendingPings()  // Clear pending pings to avoid promise leaks
             self.channel?.close(mode: .all, promise: promise)
         }
 
@@ -735,8 +737,20 @@ class ConnectionHandler: ChannelInboundHandler {
 
     private func disconnect() async throws {
         self.pingTask?.cancel()
+        clearPendingPings()  // Clear pending pings to avoid promise leaks
         try await self.channel?.close().get()
     }
+    
+    /// Clear all pending ping requests to avoid promise leaks
+    private func clearPendingPings() {
+        let pendingPings = pingQueue.dequeueAll()
+        for ping in pendingPings {
+            ping.cancel()
+        }
+        if !pendingPings.isEmpty {
+            logger.debug("Cleared \(pendingPings.count) pending ping(s)")
+        }
+    }
 
     func suspend() async throws {
         self.reconnectTask?.cancel()
@@ -746,6 +760,7 @@ class ConnectionHandler: ChannelInboundHandler {
         guard let eventLoop = self.channel?.eventLoop else {
             // Set state to suspended even if channel is nil
             self.state.withLockedValue { $0 = .suspended }
+            clearPendingPings()  // Clear pending pings to avoid promise leaks
             return
         }
         let promise = eventLoop.makePromise(of: Void.self)
@@ -759,8 +774,10 @@ class ConnectionHandler: ChannelInboundHandler {
 
             if shouldClose {
                 self.pingTask?.cancel()
+                self.clearPendingPings()  // Clear pending pings to avoid promise leaks
                 self.channel?.close(mode: .all, promise: promise)
             } else {
+                self.clearPendingPings()  // Clear pending pings even if not closing
                 promise.succeed()
             }
         }