chore: use file-scoped namespace

src/Shared/HandyControl_Shared/Controls/Base/ISelectable.cs

@@ -1,11 +1,10 @@
 using System.Windows;
 
-namespace HandyControl.Controls
-{
-    public interface ISelectable
-    {
-        event RoutedEventHandler Selected;
+namespace HandyControl.Controls;
 
-        bool IsSelected { get; set; }
-    }
-}
+public interface ISelectable
+{
+    event RoutedEventHandler Selected;
+
+    bool IsSelected { get; set; }
+}