Caching should not read forward on miss if window size constrained to 1

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Via @sorinoboroceanu
Using the caching layer when each event represents a full set of state by using a window size of 1 and a tautologous compaction predicate (see https://github.com/jet/foldunk/blob/master/Samples/Store/Domain/ContactPreferences.fs) currently has suboptimal behavior if there has been >1 competing write -- uncached, it would read exactly one event (backwards) whereas in this impl, we read all the events to catch up, but will then only use one

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For now, this has been addressed on the cosmos branch by refusing to permit the mixing of ReadStrategy.EventsAreState with the Cache.

(In Equinox.Cosmos, the Read Strategies get more powerful so implementing this facility does not fit on any reasonable roadmap, especially given the efficiency of a backward read of a single event in EventStore unless the events are of some extreme size and/or other edge cases)