One big cleanup pass of clippy lints

Co-authored-by: Mikayla <mikayla@zed.dev>

crates/gpui/src/executor.rs

@@ -332,7 +332,7 @@ impl Deterministic {
 
     pub fn now(&self) -> std::time::Instant {
         let state = self.state.lock();
-        state.now.clone()
+        state.now
     }
 
     pub fn advance_clock(&self, duration: Duration) {
@@ -681,6 +681,12 @@ impl Background {
     }
 }
 
+impl Default for Background {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 pub struct Scope<'a> {
     executor: Arc<Background>,
     futures: Vec<Pin<Box<dyn Future<Output = ()> + Send + 'static>>>,