Extend `ClientConnectionSender` with flag to indicate no reply to caller

[Centril]

So that we can disable this in fn eval_updates:

            if let Some((_, client)) = event
                .caller_address
                .zip(sender_client)
                .filter(|(addr, _)| !eval.contains_key(&(event.caller_identity, *addr)))
            {
                // Caller is not subscribed to any queries,
                // but send a transaction update with an empty subscription update.
                let update = SubscriptionUpdateMessage::default_for_protocol(client.protocol, event.request_id);
                send_to_client(client, &event, update);
            }