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/menu/menu_inner.rs

@@ -1653,7 +1653,7 @@ fn get_children_layout<Message>(
     let child_sizes: Vec<Size> = match item_height {
         ItemHeight::Uniform(u) => {
             let count = menu_tree.children.len();
-            (0..count).map(|_| Size::new(width, f32::from(u))).collect()
+            vec![Size::new(width, f32::from(u)); count]
         }
         ItemHeight::Static(s) => menu_tree
             .children

src/widget/menu/menu_tree.rs

@@ -144,7 +144,7 @@ where
     Message: std::clone::Clone + 'a,
 {
     widget::button::custom(
-        widget::Row::with_children(children)
+        widget::Row::from_vec(children)
             .align_y(Alignment::Center)
             .height(Length::Fill)
             .width(Length::Fill),
@@ -252,7 +252,7 @@ pub fn menu_items<
                     let l: Cow<'static, str> = label.into();
                     let key = find_key(&action, key_binds);
                     let mut items = vec![
-                        widget::text(l.clone()).into(),
+                        widget::text(l).into(),
                         widget::horizontal_space().into(),
                         widget::text(key).class(key_class).into(),
                     ];
@@ -272,7 +272,7 @@ pub fn menu_items<
                     let key = find_key(&action, key_binds);
 
                     let mut items = vec![
-                        widget::text(l.clone()).into(),
+                        widget::text(l).into(),
                         widget::horizontal_space().into(),
                         widget::text(key).class(key_class).into(),
                     ];