chore: use file-scoped namespace

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

@@ -1,17 +1,16 @@
 using System.Windows;
 
-namespace HandyControlDemo.UserControl
-{
-    public partial class SplitButtonDemoCtl
-    {
-        public SplitButtonDemoCtl()
-        {
-            InitializeComponent();
-        }
+namespace HandyControlDemo.UserControl;
 
-        private void ButtonBase_OnClick(object sender, RoutedEventArgs e)
-        {
-            MessageBox.Show("123");
-        }
+public partial class SplitButtonDemoCtl
+{
+    public SplitButtonDemoCtl()
+    {
+        InitializeComponent();
     }
-}
+
+    private void ButtonBase_OnClick(object sender, RoutedEventArgs e)
+    {
+        MessageBox.Show("123");
+    }
+}