Speed up itertools.pairwise

[hauntsaninja]

The pairwise implementation mentions that we can reuse the result tuple

There's currently some discussion of performance ongoing at https://discuss.python.org/t/nwise-itertools/51718

Linked PRs

• gh-118218: Reuse return tuple in itertools.pairwise #118219

[eendebakpt]

Also see #118222 (improve performance of pairwise by replacing PyTuple_Pack)