Function unzip_into_vecs 

pub(super) fn unzip_into_vecs<I, A, B>(
    pi: I,
    left: &mut Vec<A>,
    right: &mut Vec<B>,
)
where
    I: IndexedParallelIterator<Item = (A, B)>,
    A: Send,
    B: Send,

Unzips the results of the exact iterator into the specified vectors.

This is called by IndexedParallelIterator::unzip_into_vecs.