EphemeralView implementation

[DomenicDev]

This development implements the concept of an EphemeralView, a view that is built "on the fly" and not maintained/materialized. Potential use cases include:

• Lightweight aggregation for ad-hoc analysis
• Development and prototyping read models
• Building strongly consistent read models
• Supporting the "read your own rights" guarantee

The main algorithm is as follows:

suspend fun <S, E, Q, EV> EV.handle(query: Q): S where EV : ViewStateComputation<S, E>, EV : EphemeralViewRepository<E, Q> =
    query.fetchEvents().fold(initialState) { s, e -> evolve(s, e) }

Events of type E are fetched based on a query Q, which are then used to build the respective view IView<S, E>. The result of that computation S is returned to the caller.

[idugalic]

Great contribution @DomenicDev !