yoda: cargo fix --lib across all crates — drop ~115 trivial warnings

Auto-applied suggestions (unused imports, _-prefixed unused params,
redundant mutability) on iced_core, iced_widget, iced_runtime, iced_winit,
iced_wgpu, iced_graphics, iced_tiny_skia. From 170 warnings down to 55.

Leyoda 2026 – GPLv3

widget/src/lazy/component.rs

@@ -527,11 +527,11 @@ where
         renderer: &Renderer,
         dnd_rectangles: &mut core::clipboard::DndDestinationRectangles,
     ) {
-        let mut tree = tree
+        let tree = tree
             .state
             .downcast_ref::<Rc<RefCell<Option<Tree>>>>()
             .borrow_mut();
-        let mut tree = tree.as_ref().unwrap();
+        let tree = tree.as_ref().unwrap();
         self.with_element(|element| {
             element.as_widget().drag_destinations(
                 &tree.children[0],