Type safe state inheritance (#1532)

* Make state type safe

* fix examples

* remove unnecessary `#[track_caller]`s

* Router::into_service -> Router::with_state

* fixup docs

* macro docs

* add missing docs

* fix examples

* format

* changelog

* Update trybuild tests

* Make sure fallbacks are still inherited for opaque services (#1540)

* Document nesting routers with different state

* fix leftover conflicts

examples/reverse-proxy/src/main.rs

@@ -24,7 +24,7 @@ async fn main() {
 
     let client = Client::new();
 
-    let app = Router::with_state(client).route("/", get(handler));
+    let app = Router::new().route("/", get(handler)).with_state(client);
 
     let addr = SocketAddr::from(([127, 0, 0, 1], 4000));
     println!("reverse proxy listening on {}", addr);