Function wait_ack 

pub async fn wait_ack<C>(
    core: &Mutex<C>,
    notify: Arc<Notify>,
    limit: Duration,
    state: impl Fn(&C) -> (SubState, Option<String>),
) -> Result<(), Error>

Waits until the exchange has answered a subscription: Ok when it is open, [brokapi_core::Error::Rejected] (subscription_refused) when the exchange refused it, [brokapi_core::Error::Transport] when nothing came in limit.