Add HTML representation of class

[grst]

Description of feature

When typing

>>> res = DEResult(...)
>>> res

in a jupyter notebook, it would be nice to get a HTML representation of the object with some summary statistics (similar .summary())

[grst]

e.g. https://github.com/scverse/mudata/blob/22b53780eabbcff6d305f34499031200caf6bdd0/src/mudata/_core/mudata.py#L2447

--> implement _repr_html_, docs: https://ipython.readthedocs.io/en/stable/config/integrating.html