pub(crate) fn build_system<Actor1ActorSystemT, Actor2ActorSystemT>(
actor1_actor_system: Actor1ActorSystemT,
actor2_actor_system: Actor2ActorSystemT,
) -> System<Actor1ActorSystemT, Actor2ActorSystemT>where
Actor1ActorSystemT: ActorSystemHandle + Debug + Clone + Send + 'static,
Actor2ActorSystemT: ActorSystemHandle + 'static,
Actor1ActorSystemT::ActorRefT<Ping>: Clone,
Actor2ActorSystemT::ActorRefT<Actor1ToActor2<Actor1ActorSystemT::ActorRefT<Ping>>>: Clone,