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/about.rs

@@ -113,10 +113,7 @@ pub fn about<'a, Message: Clone + 'static>(
 
     let section = |list: &'a Vec<(String, String)>, title: String| {
         (!list.is_empty()).then_some({
-            let items: Vec<Element<Message>> = list
-                .iter()
-                .map(|(name, url)| section_button(name, url))
-                .collect();
+            let items = list.iter().map(|(name, url)| section_button(name, url));
             widget::settings::section().title(title).extend(items)
         })
     };