Map predicates on max time to a portion of _id

As part of the time-series schema, min time is embedded into _id. We can add the max bucket range to this to get an overestimate for max time. In addition to using the control.max.time field, we should map max time predicates to predicates on time to the min time portion of _id plus the bucket range. The 'plus' can be realized by subtracting from the user-provided predicate value in the query but we should guard against underflow. This should lead to guaranteed index utilization. This should be done inside $unpackBucket's doOptimizeAt() for $eq, $gt, $lt, $gte, $lte only.