(rchunks-exact len src)
  len: an int
  src: an arr
  returns an iter

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 len 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)