[3.13] gh-101100: Document zlib public constants to fix reference warnings (GH-139835) (#139912)

* gh-101100: Document `zlib` public constants to fix reference warnings (#139835)

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
Co-authored-by: Victor Stinner <vstinner@python.org>
(cherry picked from commit c7f1da97eb4639a17fb01ef122155bab2f262a34)

* [3.13] gh-101100: Document `zlib` public constants to fix reference warnings (GH-139835)
(cherry picked from commit c7f1da97eb4639a17fb01ef122155bab2f262a34)

Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
Co-authored-by: Victor Stinner <vstinner@python.org>

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Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
Co-authored-by: Victor Stinner <vstinner@python.org>