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/async-graphql/src/main.rs

@@ -34,7 +34,9 @@ async fn main() {
         .data(StarWars::new())
         .finish();
 
-    let app = Router::with_state(schema).route("/", get(graphql_playground).post(graphql_handler));
+    let app = Router::new()
+        .route("/", get(graphql_playground).post(graphql_handler))
+        .with_state(schema);
 
     println!("Playground: http://localhost:3000");