Replace broker broadcast messages with directed equivalents where appropriate

[mycognosist]

For example, the connection_scheduler actor could be sending messages addressed directly to the dialer actor (instead of sending on the broadcast channel).

This is an optimisation and not urgent in any way.

[mycognosist]

In order for this to be possible we'll probably have to identify actors via their name and not their broker-assigned ID, since the ID assigned to an actor can not be known ahead of time. Note, however, that this name-based approach will only work for actors which are only spawned once (ie. the dialer or connection-scheduler, but not connection or classic replication actor).

Add actor_name field to BrokerEndpoint and match on it in the message loop when handling a BrokerEvent::Message.

https://github.com/mycognosist/solar/blob/main/solar/src/broker.rs#L227