Fix remaining compilation errors: null-safety, removed packages, and nullable handling

- Fix AppState: remove removed connectivity package, fix imports (latlong2), make nullable fields optional
- Fix User model: use const empty strings in const constructor instead of null
- Fix model builders: add required ObjectId parameters to YourLocation and FireNotification
- Implement Comparable instead of extending it for BasicLocation
- Fix nullable callback handling in appActions and middleware (Completer<Null>?)
- Add null checks for BuildContext in dialogs (fireAlert, homePage, etc.)
- Fix nullable scaffold state access using ?. operator (activeFires, fireNotificationList)
- Handle nullable FireNotification and YourLocation in genericMapBottom
- Fix list type casting for widgets that can be null (<Widget?> with filtering)
- Add ObjectId imports where needed for model creation
- Fix Key? nullable parameter in introPage
- Add required parameters to markdownPage and slider constructors
- Remove connectivity-related code and imports (package removed)
- Handle nullable Completer in fetchDataMiddleware

All 104 errors resolved. 0 errors, 61 warnings/info remaining.

lib/models/fireNotificationsPersist.dart

@@ -10,13 +10,14 @@ final String fireNotificationKey = 'fireNotifications';
 
 Future<List<FireNotification>> loadFireNotifications() async {
   return await globals.prefs.then((prefs) {
-    List<String> FireNotifications = prefs.getStringList(fireNotificationKey);
+    List<String>? FireNotifications = prefs.getStringList(fireNotificationKey);
     List<FireNotification> persistedList = [];
-    FireNotifications.forEach((notificationString) {
+    (FireNotifications ?? []).forEach((notificationString) {
       Map notificationMap = json.decode(notificationString);
-      persistedList.add(FireNotification.fromJson(notificationMap));
+      persistedList.add(
+          FireNotification.fromJson(notificationMap as Map<String, dynamic>));
     });
-      return persistedList;
+    return persistedList;
   });
 }