Fix 13 lint issues: immutability, imports, async/await, and code style

High-priority fixes (10 issues):
- assignment_to_final errors (7): Use copyWith() to respect immutability in YourLocation, active_fires.dart, generic_map.dart, location_utils.dart, and fetch_data_middleware.dart instead of direct assignment
- Fixed import paths (3): Updated falsePositiveTypes.dart → false_positive_types.dart and firesApi.dart → fires_api.dart in reducers.dart, fire_notification_actions.dart, fires_api.dart

Medium/Low priority fixes (3 issues):
- unnecessary_non_null_assertion: Removed redundant '!' in app_intro_page.dart line 54
- use_super_parameters: Updated app_intro_page.dart to use modern super(key: key) syntax
- no_logic_in_create_state: Fixed material_app_with_intro.dart by moving parameters to State instead of createState
- noop_primitive_operations: Removed redundant .toString() in string interpolation
- avoid_void_async: Changed void _selectLocation to Future<void> in places_autocomplete_utils.dart
- avoid_dynamic_calls: Fixed dynamic map access in fires_api.dart by properly casting intermediate values

Result: Reduced lint issues from 56 to 20 (all remaining are by-design: library_private_types_in_public_api and implementation_imports from external packages)
APK builds successfully with no errors.

lib/places_autocomplete_utils.dart

@@ -65,7 +65,7 @@ class _PlaceSelectionDialogState extends State<_PlaceSelectionDialog> {
       });
     } catch (e) {
       setState(() {
-        _errorMessage = 'Search error: ${e.toString()}';
+        _errorMessage = 'Search error: $e';
         _searchResults = <Location>[];
       });
     } finally {
@@ -98,7 +98,7 @@ class _PlaceSelectionDialogState extends State<_PlaceSelectionDialog> {
     return '${location.latitude.toStringAsFixed(4)}, ${location.longitude.toStringAsFixed(4)}';
   }
 
-  void _selectLocation(Location location) async {
+  Future<void> _selectLocation(Location location) async {
     final String description = await _getPlaceName(location);
     if (!mounted) {
       return;