chore: use file-scoped namespace

src/Shared/HandyControlDemo_Shared/UserControl/Controls/RelativePanelDemoCtl.xaml.cs

@@ -1,10 +1,9 @@
-namespace HandyControlDemo.UserControl
+namespace HandyControlDemo.UserControl;
+
+public partial class RelativePanelDemoCtl
 {
-    public partial class RelativePanelDemoCtl
+    public RelativePanelDemoCtl()
     {
-        public RelativePanelDemoCtl()
-        {
-            InitializeComponent();
-        }
+        InitializeComponent();
     }
-}
+}