Use captured identifiers in format strings.

This was stabilized in Rust 1.58.0: https://blog.rust-lang.org/2022/01/13/Rust-1.58.0.html

example-service/src/server.rs

@@ -40,7 +40,7 @@ impl World for HelloServer {
         let sleep_time =
             Duration::from_millis(Uniform::new_inclusive(1, 10).sample(&mut thread_rng()));
         time::sleep(sleep_time).await;
-        format!("Hello, {}! You are connected from {}", name, self.0)
+        format!("Hello, {name}! You are connected from {}", self.0)
     }
 }