Extract Suspendable interface from SuspendableEventStream.
Ditch error reporting mechanism.
Remove Subscriber interface. Use Consumer again.
Facilitate better code reuse:

Extract methods from class EventStreamBase to interface EventStreamHelpers
as default methods.
Extract SuspendableBase from SuspendableEventStreamBase.
Add AccumulationFacility mixins. Refactor AccuMap.
DRY: By default, reuse NotificationAccumulator's AccumulationFacility for accumulation while suspended.