Retain request dependencies only when discovery supplies the answer

core/src/widget/widgets.rs

@@ -128,8 +128,8 @@ impl Widgets {
     }
 
     /// The length rules whoever draws this widget applies to its box.
-    pub fn size_rules(&self, id: impl IdLike) -> SizeRules {
-        self.data(id).unwrap().size.clone()
+    pub fn size_rules(&self, id: impl IdLike) -> &SizeRules {
+        &self.data(id).unwrap().size
     }
 
     /// Sets one axis's rule. The widget is marked rather than its parent