Implement nested object selection and placement for NCOPY

src/command.rs

@@ -1940,6 +1940,8 @@ impl InputKind {
 }
 
 pub trait CadCommand: Send {
+    /// Preserve source appearance for commands that extract existing entities.
+    fn preserve_commit_style(&self) -> bool { false }
     /// Keep the layer already carried by entities committed by this command
     /// instead of replacing it with the current drawing layer.
     fn preserve_commit_layer(&self) -> bool {