style(demos): file-scoped namespace + reindent DemoPickable

Disp/DemoPickable.cs

@@ -2,8 +2,8 @@
 using Hi.Geom;
 using System;
 
-namespace Sample.Disp
-{
+namespace Sample.Disp;
+
 /// <summary>
 /// Demonstrates creation of pickable 3D geometry at the primitive level.
 /// Shows how to assign picking IDs directly to geometry vertices and create interactive triangles.
@@ -56,6 +56,3 @@ namespace Sample.Disp
 		DemoUtil.RunApplication("DemoPickable", new DemoPickable());
 	}
 }
-
-
-}