Iterates over non-overlapping sub-arrays with an exact size, in reverse order.
Each array produced by the iterator is newly-allocated and mutable, with exactly
elements. If the length of
src is not an exact multiple of
len, some of its
elements will be skipped.
(prn ..(rchunks-exact 2 '(0 1 2 3 4))) ; prints (3 4) (1 2)