event_source and event_sink are two abstractions we have around event_store.
Event stream processor should use event_source to subscribe and read events, and use event_sink to emit new events.
Let's replace event_store in EventProcessing namespace with event_source
event_sourceandevent_sinkare two abstractions we have aroundevent_store. Event stream processor should useevent_sourceto subscribe and read events, and useevent_sinkto emit new events. Let's replaceevent_storein EventProcessing namespace withevent_source