Add revision fuzzing for picking optimized revisions

[jakedt]

Right now when a new optimized revision becomes the de-facto choice, the entire existing cache is (practically) simultaneously invalidated. In order to decrease the effect of this cutover, we should probably phase between the outgoing optimized revision and the incoming optimized revision over some period of time. Other revision picking logic, such as AtLeastAsFresh consistency happens after the optimized revision picking and should therefore be unaffected.