chore: use file-scoped namespace

src/Shared/HandyControlDemo_Shared/ViewModel/Controls/SplitButtonDemoViewModel.cs

@@ -2,10 +2,9 @@
 using GalaSoft.MvvmLight.Command;
 using HandyControl.Controls;
 
-namespace HandyControlDemo.ViewModel
+namespace HandyControlDemo.ViewModel;
+
+public class SplitButtonDemoViewModel : ViewModelBase
 {
-    public class SplitButtonDemoViewModel : ViewModelBase
-    {
-        public RelayCommand<string> SelectCmd => new(str => Growl.Info(str));
-    }
-}
+    public RelayCommand<string> SelectCmd => new(str => Growl.Info(str));
+}