- Add Linter rules for return types and final fields

- Enhance exception_handler code
- Add ShareUtil to unify modification point

lib/utils/share_util.dart

@@ -0,0 +1,13 @@
+import 'package:flutter/material.dart';
+import 'package:share_plus/share_plus.dart';
+
+class ShareUtil {
+  static void share({required String text, required BuildContext context}) {
+    final box = context.findRenderObject() as RenderBox?;
+
+    Share.share(
+      text,
+      sharePositionOrigin: box!.localToGlobal(Offset.zero) & box.size,
+    );
+  }
+}