Fix missing lifetime warnings

Author: djc

metrics/src/key.rs

@@ -132,7 +132,7 @@ impl Key {
     }
 
     /// Labels of this key, if they exist.
-    pub fn labels(&self) -> Iter<Label> {
+    pub fn labels(&self) -> Iter<'_, Label> {
         self.labels.iter()
     }
 

metrics/src/recorder/mod.rs

@@ -203,7 +203,7 @@ where
 ///
 /// If a global recorder is set, it will be restored once the guard is dropped.
 #[must_use]
-pub fn set_default_local_recorder(recorder: &dyn Recorder) -> LocalRecorderGuard {
+pub fn set_default_local_recorder(recorder: &dyn Recorder) -> LocalRecorderGuard<'_> {
     LocalRecorderGuard::new(recorder)
 }