perf: reduce memory allocations

This also changes `widget::column::with_children` and
`widget::row::with_children` to take an `impl IntoIterator` instead
of a `Vec`, like the `iced` variants of these functions do.

This shouldn't be a breaking change since passing in a `Vec` will still
compile and function exactly as before.

(Using `iced::widget::Column::from_vec` or
`iced::widget::Row::from_vec` isn't possible, since the elements of the
`Vec` aren't checked, so the size of the resulting `Column` or `Row`
won't adapt to the size of its children. Perhaps a new function could
be added to mirror `iced`'s?)

src/widget/segmented_button/widget.rs

@@ -274,7 +274,7 @@ where
         self.on_dnd_drop = Some(Box::new(move |entity, data, mime, action| {
             dnd_drop_handler(entity, D::try_from((data, mime)).ok(), action)
         }));
-        self.mimes = D::allowed().iter().cloned().collect();
+        self.mimes = D::allowed().into_owned();
         self
     }
 
@@ -1867,7 +1867,7 @@ fn draw_icon<Message: 'static>(
     });
 
     Widget::<Message, crate::Theme, Renderer>::draw(
-        Element::<Message>::from(icon.clone()).as_widget(),
+        Element::<Message>::from(icon).as_widget(),
         &Tree::empty(),
         renderer,
         theme,