The extract_markdown stub was calling extract_text instead of
extract_text_fn, causing a compilation error. This fixes the
function name to match the exported function from extract_text.rs.
This completes the extract_text PyO3 entry point implementation,
which was already present in extract_text.rs and lib.rs.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
