Function init 

pub fn init<E, F, Con, P>(
    context: E,
    fetcher: F,
    consumer: Con,
    mailbox_size: NonZeroUsize,
    fetch_retry_timeout: Duration,
) -> Resolver<F::Key, Con::Subscriber, P>
where
    E: Clock + Spawner + Metrics,
    F: Fetcher + Clone + Send + 'static,
    F::Value: Clone + Send + 'static,
    Con: Consumer<Key = F::Key, Value = F::Value>,
    Con::Subscriber: Ord,
    P: PublicKey,

Spawn an opaque-fetcher resolver actor.