Fix further clippy lints

... and explicitly annotate crates as well.

futures/src/subscription/tracker.rs

@@ -156,3 +156,13 @@ where
             });
     }
 }
+
+impl<Hasher, Event> Default for Tracker<Hasher, Event>
+where
+    Hasher: std::hash::Hasher + Default,
+    Event: 'static + Send + Clone,
+{
+    fn default() -> Self {
+        Self::new()
+    }
+}