DOC: inline math expressions not rendered correctly

[kay-ro]

Problem description:

The api reference of several methods has incorrectly rendered inline math expressions. Example:

Suggested content improvement:

• [ ] https://amepproject.de/_autosummary/amep.cluster.radius_of_gyration.html
• [ ] https://amepproject.de/_autosummary/amep.continuum.coords_to_density.html
• [ ] https://amepproject.de/_autosummary/amep.continuum.sf2d.html
• [ ] https://amepproject.de/_autosummary/amep.order.psi_k.html
• [ ] https://amepproject.de/_autosummary/amep.spatialcor.pcf2d.html
• [ ] https://amepproject.de/_autosummary/amep.spatialcor.sf2d.html
• [ ] https://amepproject.de/_autosummary/amep.spatialcor.spatialcor.html
• [ ] ... check all docstrings