Add scroll queue detection in notification view

This will stop injecting events into the timeline if you're scrolling

damus/Models/NotificationsModel.swift

@@ -45,7 +45,8 @@ enum NotificationItem {
     }
 }
 
-class NotificationsModel: ObservableObject {
+class NotificationsModel: ObservableObject, ScrollQueue {
+    
     var incoming_zaps: [Zap]
     var incoming_events: [NostrEvent]
     var should_queue: Bool
@@ -73,6 +74,10 @@ class NotificationsModel: ObservableObject {
         self.notifications = []
     }
     
+    func set_should_queue(_ val: Bool) {
+        self.should_queue = val
+    }
+    
     func uniq_pubkeys() -> [String] {
         var pks = Set<String>()