Fix high-signal widget and Wayland warnings

Avoid recursive operation traversal, execute visible list updates instead of leaving a lazy iterator unused, remove unreachable cfg-gated surface creation code, and handle subsurface buffer attachment failures.

widget/src/container.rs

@@ -601,7 +601,7 @@ pub fn visible_bounds(id: Id) -> Task<Option<Rectangle>> {
             operate: &mut dyn FnMut(&mut dyn Operation<Option<Rectangle>>),
         ) {
             self.depth += 1;
-            self.traverse(operate);
+            operate(self);
             self.depth -= 1;
         }
 

widget/src/list.rs

@@ -366,7 +366,7 @@ where
         self.visible_elements
             .iter_mut()
             .zip(&mut state.visible_layouts)
-            .map(|(element, (index, layout, tree))| {
+            .for_each(|(element, (index, layout, tree))| {
                 element.as_widget_mut().update(
                     tree,
                     event,