Reduce overhead of PartitionedRegion.executeOnBucketSet

PartitionedRegion.executeOnBucketSet spends 56% of function executions CPU time comparing and pruning bucket sets. It also accounts for 89% of the transient object allocation during function execution.

Given that bucket sets are sets of integers let's look for a more suitable implementation of set operations on integers. Consider int[] as set of integers too reduce CPU and transient object allocations.