fix: must_use the structs

benches/bench.rs

@@ -6,6 +6,7 @@ use ratatui::layout::Rect;
 use ratatui::widgets::StatefulWidget;
 use tui_tree_widget::{Tree, TreeItem, TreeState};
 
+#[must_use]
 fn example_items() -> Vec<TreeItem<'static, &'static str>> {
     vec![
         TreeItem::new_leaf("a", "Alfa"),
@@ -73,15 +74,15 @@ fn init(criterion: &mut Criterion) {
 
     group.bench_function("empty", |bencher| {
         bencher.iter(|| {
-            let items: Vec<TreeItem<usize>> = vec![];
-            black_box(Tree::new(black_box(&items))).unwrap();
+            let items = vec![];
+            let _: Tree<usize> = black_box(Tree::new(black_box(&items))).unwrap();
         });
     });
 
     group.bench_function("example-items", |bencher| {
         bencher.iter(|| {
             let items = example_items();
-            black_box(Tree::new(black_box(&items))).unwrap();
+            let _: Tree<_> = black_box(Tree::new(black_box(&items))).unwrap();
         });
     });