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/placesAutocompleteUtils.dart

@@ -109,7 +109,6 @@ class _PlaceSelectionDialogState extends State<_PlaceSelectionDialog> {
       lat: location.latitude,
       lon: location.longitude,
       description: description,
-      distance: 10,
     );
 
     Navigator.of(context).pop(yourLocation);