Fix keyexpr_tree lifetime (#1452)

commons/zenoh-keyexpr/src/keyexpr_tree/traits/mod.rs

@@ -27,7 +27,7 @@ pub trait IKeyExprTree<'a, Weight> {
     /// Accesses the node at `key` if it exists, treating KEs as if they were completely verbatim keys.
     ///
     /// Returns `None` if `key` is not present in the KeTree.
-    fn node(&'a self, key: &keyexpr) -> Option<&Self::Node>;
+    fn node(&'a self, key: &keyexpr) -> Option<&'a Self::Node>;
 
     /// Returns a reference to the weight of the node at `key` if it exists.
     fn weight_at(&'a self, key: &keyexpr) -> Option<&'a Weight> {