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/widgets/rounded_btn.dart

@@ -3,15 +3,6 @@ import 'package:flutter/material.dart';
 /// Rounded button widget with icon and text.
 /// Used primarily in the active fires page.
 class RoundedBtn extends StatelessWidget {
-  static const btnRadius = Radius.circular(90.0);
-
-  final IconData icon;
-  final String text;
-  final Color backColor;
-  final Color fontColor;
-  final TextStyle textStyle;
-  final VoidCallback onPressed;
-
   const RoundedBtn({
     required this.icon,
     required this.text,
@@ -42,6 +33,15 @@ class RoundedBtn extends StatelessWidget {
     );
   }
 
+  static const Radius btnRadius = Radius.circular(90.0);
+
+  final IconData icon;
+  final String text;
+  final Color backColor;
+  final Color fontColor;
+  final TextStyle textStyle;
+  final VoidCallback onPressed;
+
   @override
   Widget build(BuildContext context) {
     return SizedBox(
@@ -49,7 +49,7 @@ class RoundedBtn extends StatelessWidget {
         onPressed: onPressed,
         style: ElevatedButton.styleFrom(
           backgroundColor: backColor,
-          shape: RoundedRectangleBorder(
+          shape: const RoundedRectangleBorder(
             borderRadius: BorderRadius.all(btnRadius),
           ),
         ),