Bump package versions to 0.3.0 across most packages; update navigation_rail_m3e to 0.3.2, add new features, enhancements, and documentation to navigation_rail_m3e. Update melos.yaml with new scripts. Refactor update_versions.dart script.

packages/navigation_rail_m3e/example/lib/main.dart

@@ -5,7 +5,9 @@ void main() {
   runApp(const DemoApp());
 }
 
+/// Simple demo application for NavigationRailM3E.
 class DemoApp extends StatefulWidget {
+  /// Creates the demo app widget.
   const DemoApp({super.key});
   @override
   State<DemoApp> createState() => _DemoAppState();