Get message status

Get the delivery and engagement status of a push notification message. **Features:** - Track delivery status per device token - Monitor open and click events - View detailed statistics - Error tracking and debugging **Status Types:** - **pending**: Message queued but not sent - **sent**: Message sent to FCM successfully - **delivered**: Message delivered to device - **opened**: User opened the notification - **clicked**: User clicked the notification - **failed**: Message failed to send - **expired**: Message expired (TTL reached) **Use Cases:** - Campaign analytics - Delivery monitoring - User engagement tracking - Debugging failed deliveries