[3.13] gh-141004: Document `pyctype.h` macros (GH-141272) (GH-141339)

gh-141004: Document `pyctype.h` macros (GH-141272)
(cherry picked from commit df192616212f80aaa2f672b722b925943dbd3b78)

Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>