chore: Clippy lints and compile fixes.

src/system/condvar.rs

@@ -72,6 +72,12 @@ impl CondVar {
     }
 }
 
+impl Default for CondVar {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 pub struct CondVarWait<'a> {
     state: &'a Mutex<CondVarState>,
 }

src/system/lazy_weak.rs

@@ -91,3 +91,9 @@ impl<Parent> LazyWeak<Parent> {
         self.0.get().unwrap().upgrade().unwrap()
     }
 }
+
+impl<Parent> Default for LazyWeak<Parent> {
+    fn default() -> Self {
+        Self::new()
+    }
+}