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/redux/fireMapReducer.dart

@@ -1,5 +1,6 @@
 import 'package:redux/redux.dart';
 import 'package:fires_flutter/models/yourLocation.dart';
+import 'package:objectid/objectid.dart';
 import '../models/fireMapState.dart';
 import 'actions.dart';
 
@@ -7,7 +8,7 @@ final fireMapReducer = combineReducers<FireMapState>([
   new TypedReducer<FireMapState, ShowYourLocationMapAction>(
       _showYourLocationMap),
   new TypedReducer<FireMapState, ShowFireNotificationMapAction>(
-    _showFireNotificationMap),
+      _showFireNotificationMap),
   new TypedReducer<FireMapState, UpdateFireMapStatsAction>(
       _updateYourLocationMapStats),
   new TypedReducer<FireMapState, SubscribeAction>(_subscribeYourLocationMap),
@@ -20,8 +21,7 @@ final fireMapReducer = combineReducers<FireMapState>([
       _editConfirmYourLocationMap),
   new TypedReducer<FireMapState, EditCancelYourLocationAction>(
       _editCancelYourLocationMap),
-  new TypedReducer<FireMapState, ToggleMapLayerAction>(
-    _toggleMapLayer),
+  new TypedReducer<FireMapState, ToggleMapLayerAction>(_toggleMapLayer),
   new TypedReducer<FireMapState, UpdateYourLocationMapAction>(
       _updateYourLocationMap)
 ]);
@@ -46,15 +46,22 @@ FireMapState _showYourLocationMap(
       status: action.loc.subscribed
           ? FireMapStatus.unsubscribe
           : FireMapStatus.view,
-      yourLocation: action.loc, fireNotication: null);
+      yourLocation: action.loc,
+      fireNotication: null);
 }
 
 FireMapState _showFireNotificationMap(
     FireMapState state, ShowFireNotificationMapAction action) {
   // TODO: use here you real location?
-  YourLocation pseudoLoc = new YourLocation(lat: action.notif.lat, lon: action.notif.lon, description: action.notif.description);
+  YourLocation pseudoLoc = new YourLocation(
+      id: ObjectId(),
+      lat: action.notif.lat,
+      lon: action.notif.lon,
+      description: action.notif.description);
   return state.copyWith(
-      status: FireMapStatus.viewFireNotification, yourLocation: pseudoLoc, fireNotication: action.notif);
+      status: FireMapStatus.viewFireNotification,
+      yourLocation: pseudoLoc,
+      fireNotication: action.notif);
 }
 
 FireMapState _subscribeYourLocationMap(
@@ -92,12 +99,12 @@ FireMapState _editCancelYourLocationMap(
 FireMapStatus restoreStatusAfterSave(loc) =>
     loc.subscribed ? FireMapStatus.unsubscribe : FireMapStatus.view;
 
-FireMapState _toggleMapLayer(
-  FireMapState state, ToggleMapLayerAction action) {
+FireMapState _toggleMapLayer(FireMapState state, ToggleMapLayerAction action) {
   FireMapLayer currentLayer = state.layer;
   List<FireMapLayer> list = FireMapLayer.values;
   int currentPos = list.indexOf(currentLayer);
   currentPos++;
-  FireMapLayer next = list.elementAt(currentPos >= list.length ? 0: currentPos);
+  FireMapLayer next =
+      list.elementAt(currentPos >= list.length ? 0 : currentPos);
   return state.copyWith(layer: next);
-}
+}