Enable doctesting for all narrative documentations

Some modules still don't have doctest enabled on their narrative docs. Quick grep for `doctest-skip-all` brings up this list (some may be irrelevant for doctesting, I'll remove those from the list later).

- [ ] docs/api.rst
- [ ] docs/astrometry_net/astrometry_net.rst
- [ ] docs/besancon/besancon.rst
- [ ] docs/cosmosim/cosmosim.rst
- [ ] docs/gaia/gaia.rst
- [ ] docs/image_cutouts/first/first.rst
- [ ] docs/image_cutouts/image_cutouts.rst
- [ ] docs/ipac/irsa/ibe/ibe.rst
- [ ] docs/mocserver/mocserver.rst
- [ ] docs/query.rst
- [x] docs/simbad/simbad.rst
- [ ] docs/testing.rst
- [ ] docs/ukidss/ukidss.rst
- [ ] docs/utils.rst
- [ ] docs/utils/tap.rst
- [ ] docs/vamdc/vamdc.rst
- [x] docs/vizier/vizier.rst
- [ ] docs/vo_conesearch/client.rst
- [ ] docs/vo_conesearch/validator.rst
- [ ] docs/vo_conesearch/vo_conesearch.rst
- [ ] docs/vsa/vsa.rst
- [ ] docs/wfau/wfau.rst

Start by checking the listed .rst files for doctest-skip-all, using the existing docs/simbad/simbad.rst and docs/vizier/vizier.rst entries as completed examples. Confirm which files are relevant for doctesting, enable it for the remaining applicable narrative documentation, and verify the documentation doctests pass.

Written by the indexing model from the issue text.