Use updated Service trait for ntex (#456)

ntex-service/src/lib.rs

@@ -120,6 +120,10 @@ pub trait Service<Req> {
 
     #[inline]
     /// Returns when the service is not able to process requests.
+    ///
+    /// Unlike the "ready()" method, the "not_ready()" method returns
+    /// only when the service becomes unready. This method is intended
+    /// for actively monitoring and maintaining the service state.
     async fn not_ready(&self) {
         std::future::pending().await
     }