Sink/NoOp entities

[beylerian]

It could be useful to have some "no-op" entities that act as loop/sinks in some situations, where we need to define them but have no state mutation.

For example

object SinkState : State

object SinkReducer : Reducer<State> {
    override fun reduce(currentState: State, action: Action): State = SinkState
}

object NoOpReducer : Reducer<State> {
    override fun reduce(currentState: State, action: Action): State = currentState
}