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/yourLocation.dart

@@ -6,9 +6,10 @@ import '../objectIdUtils.dart';
 
 part 'yourLocation.g.dart';
 
+@immutable
 @JsonSerializable()
 class YourLocation {
-  YourLocation(
+  const YourLocation(
       {required this.id,
       required this.lat,
       required this.lon,
@@ -24,10 +25,10 @@ class YourLocation {
   final ObjectId id;
   final double lat;
   final double lon;
-  String description;
-  bool subscribed;
-  int distance;
-  int currentNumFires;
+  final String description;
+  final bool subscribed;
+  final int distance;
+  final int currentNumFires;
 
   static YourLocation get noLocation {
     _noLocation ??= YourLocation(id: ObjectId(), lat: 0.0, lon: 0.0);