Fix 23 additional lint issues to reduce from 129 to 106 issues

- Add const constructors to @immutable classes (5 issues: prefer_const_constructors_in_immutables)
- Fix nullable value casts in firesApi.dart (3 issues: cast_nullable_to_non_nullable)
- Remove redundant default argument values (2 issues: avoid_redundant_argument_values)
- Make YourLocation immutable with final fields (2 issues: avoid_equals_and_hash_code_on_mutable_classes)
- Update imports and fix formatting

Reduces lint issues from 129 to 106. APK builds successfully (146 MB).

lib/models/basicLocation.dart

@@ -4,7 +4,7 @@ import 'package:meta/meta.dart';
 class BasicLocation implements Comparable<BasicLocation> {
 //  static BasicLocation noLocation = new BasicLocation(lat: 0.0, lon: 0.0);
 
-  BasicLocation({required this.lat, required this.lon, this.description});
+  const BasicLocation({required this.lat, required this.lon, this.description});
 
   BasicLocation.fromJson(Map<String, dynamic> json)
       : lat = (json['lat'] as num).toDouble(),