Change Router::with_state and impl Service for Router<()> (#1552)

* Implement `Service` for `Router<(), B>`

* wip

* wip

* fix some tests

* fix examples

* fix doc tests

* clean up docs

* changelog

* fix

* also call `with_state` when converting `MethodRouter` into a `MakeService`

* suggestions from review

axum-extra/src/routing/resource.rs

@@ -147,7 +147,7 @@ impl<B> From<Resource<B>> for Router<B> {
 mod tests {
     #[allow(unused_imports)]
     use super::*;
-    use axum::{extract::Path, http::Method, routing::RouterService, Router};
+    use axum::{extract::Path, http::Method, Router};
     use http::Request;
     use tower::{Service, ServiceExt};
 
@@ -162,7 +162,7 @@ mod tests {
             .update(|Path(id): Path<u64>| async move { format!("users#update id={}", id) })
             .destroy(|Path(id): Path<u64>| async move { format!("users#destroy id={}", id) });
 
-        let mut app = Router::new().merge(users).into_service();
+        let mut app = Router::new().merge(users);
 
         assert_eq!(
             call_route(&mut app, Method::GET, "/users").await,
@@ -205,7 +205,7 @@ mod tests {
         );
     }
 
-    async fn call_route(app: &mut RouterService, method: Method, uri: &str) -> String {
+    async fn call_route(app: &mut Router, method: Method, uri: &str) -> String {
         let res = app
             .ready()
             .await

axum-extra/src/routing/spa.rs

@@ -270,7 +270,7 @@ mod tests {
 
     #[allow(dead_code)]
     fn works_with_router_with_state() {
-        let _: axum::RouterService = Router::new()
+        let _: Router = Router::new()
             .merge(SpaRouter::new("/assets", "test_files"))
             .route("/", get(|_: axum::extract::State<String>| async {}))
             .with_state(String::new());