Always store state in an Arc (#1270)

* Add extension and state benchmarks

* wip

* Arc the state everywhere

* don't require `S: Clone`

* fix example

examples/jwt/src/main.rs

@@ -124,7 +124,7 @@ impl AuthBody {
 #[async_trait]
 impl<S, B> FromRequest<S, B> for Claims
 where
-    S: Send,
+    S: Send + Sync,
     B: Send,
 {
     type Rejection = AuthError;