Clean up "References" reST directives

Nobody has claimed this yet.

TIL that the "References" section should have footnote-style directives.

e.g.

```
"""Create a Passband object from the SVO [1]_, [2]_, [3]_ Filter Profile Service.

References
----------
.. [1] Rodrigo, C., Cruz, P., Aguilar, J.F., et al. 2024;
https://ui.adsabs.harvard.edu/abs/2024A%26A...689A..93R/abstract

.. [2] Rodrigo, C., Solano, E., Bayo, A., 2012;
https://ui.adsabs.harvard.edu/abs/2012ivoa.rept.1015R/abstract

.. [3] Rodrigo, C., Solano, E., 2020; https://ui.adsabs.harvard.edu/abs/2020sea..confE.182R/abstract

```

This results in a really nice rendering via read the docs:

The `.. [1] ` kind of text at the beginning of those lines can be removed for ease of copy/paste.

See:
https://numpydoc.readthedocs.io/en/latest/format.html#references

Search the repository for docstrings with a References section and the `.. [1]`-style directives shown in the issue. Compare their formatting with the linked numpydoc guidance and confirm the rendered documentation preserves the intended footnote presentation while making the reference text easier to copy and paste.

Written by the indexing model from the issue text.