partition()/chunks() on an iterator (_cut_iter) only correctly skipped
step items between parts when step <= n. For step > n, slicing an
n-length pool by pool[step:] silently clips to an empty list, then
islice(it, step) pulled step (not n) fresh items into the pool instead
of first discarding the step - n items between parts. This produced
wrong-length, wrong-content chunks that diverged from the Sequence
code path (_cut_seq) for the same input, e.g. list(range(10)) vs
iter(range(10)) with n=2, step=3.
Branch on step < n to keep the existing sliding-window logic, and for
step >= n explicitly discard the gap before taking the next pool.
dualfroz
a12abd3a5e