chore: Update min Dart constraint to 3.8 (#3676)

Update min Dart constraint to 3.8, which will enable us to use the
fancier collection literals.

This requires bumping the min Flutter version as well:

<img width="1892" height="1122" alt="image"
src="https://github.com/user-attachments/assets/7c7b07fc-4d96-4987-824d-9a7133ecfb85"
/>

examples/lib/stories/components/components_notifier_provider_example.dart

@@ -80,10 +80,10 @@ class GameHud extends StatelessWidget {
 
 class Enemy extends CircleComponent with TapCallbacks, Notifier {
   Enemy({super.position})
-      : super(
-          radius: 20,
-          paint: Paint()..color = const Color(0xFFFF0000),
-        );
+    : super(
+        radius: 20,
+        paint: Paint()..color = const Color(0xFFFF0000),
+      );
 
   @override
   void onTapUp(_) {