Resolve "Update Sphinx setup to be able to use the ipython directive"

This MR adds the IPython directive to the sphinx configuration and tests it out on a part of the configuration.

Can this MR be accepted?

• Adjust Sphinx configuration to use the IPython directive
• Documentation extended or updated
  • Test out usage on the data_structures/groups/psp.rst page (it's super convenient!)
  • Add a section on "Universes and Multiverses" (was missing)
  • Remove empty / WIP page on "multidimensional data"
• No code changes (except tested includes)

• Ready for merging
  • Pipeline passes without warnings
  • History cleaned-up or squash option set
  • Changelog entry added
  • Version number bumped
  • Reviewed & approved by @jeremiastraub

Related issues

Closes #188 (closed)