fn execute<I, OP, FromA, FromB>(pi: I, op: OP) -> (FromA, FromB)where
    I: ParallelIterator,
    OP: UnzipOp<I::Item>,
    FromA: Default + Send + ParallelExtend<OP::Left>,
    FromB: Default + Send + ParallelExtend<OP::Right>,Expand description
Runs an unzip-like operation into default ParallelExtend collections.