seat: handle surface cursor lifetimes explicitly

src/cursor.rs

@@ -60,6 +60,7 @@ pub trait Cursor {
     fn set_output(&self, output: &Rc<OutputNode>) {
         let _ = output;
     }
+    fn handle_set(self: Rc<Self>) {}
     fn handle_unset(&self) {}
     fn tick(&self) {}
     fn needs_tick(&self) -> bool {