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/table/widget/compact.rs

@@ -170,7 +170,6 @@ where
                     )
                     .apply(Element::from)
             })
-            .collect::<Vec<Element<'a, Message>>>()
             .apply(widget::column::with_children)
             .spacing(val.item_spacing)
             .padding(val.element_padding)

src/widget/table/widget/standard.rs

@@ -125,7 +125,6 @@ where
                     .apply(|mouse_area| widget::context_menu(mouse_area, cat_context_tree))
                     .apply(Element::from)
             })
-            .collect::<Vec<Element<'a, Message>>>()
             .apply(widget::row::with_children)
             .apply(Element::from);
         // Build the items
@@ -166,7 +165,6 @@ where
                                     .align_y(Alignment::Center)
                                     .apply(Element::from)
                             })
-                            .collect::<Vec<Element<'static, Message>>>()
                             .apply(widget::row::with_children)
                             .apply(container)
                             .padding(val.item_padding)