Add summary function

[aloctavodia]

Closes #11

This adds the basic functionality for the summary function. It is still not on par with the summary function from old ArviZ, but it is better than nothing. Currently, the output is a dataset. To get a Pandas' DataFrame we need arviz-devs/arviz-base#25

In the old arviz we had a kind argument and a stat_focus argument. The combination of both specifies which stats/diagnostics were computed. Now we achieve the same with just the kind argument. For instance kind="all" is the equivalent of the old kind=all and stats_focus="mean" and kind kind="all_median" is the equivalent of the old kind=all and stats_focus="median". Having a single argument seems clear to me.

One source of inconsistency is that previously we returned the hdi if stat_focus="mean" and the eti if stat_focus="median . But in arviz 1.0 whether to compute these two different CI depend on a global rcparam value. Should we ignore the rcparam specification and return what the kind argument dictates? If "stats_median", or "all_median" we return eti irrespective of the value of ci_kind (or the value in rcparams).

---

📚 Documentation preview 📚: https://arviz-stats--51.org.readthedocs.build/en/51/

[amaloney]

tag me when you are ready for a review

[amaloney]

This looks great. Just a few nits about the docstring and type-hints, if you are okay with the suggested changes.

The only thing I would request an actual change for is the default value in the docstring does not match that in the function signature.

[aloctavodia]

I fixed the docstring and added type hints.

Please check if they are ok, feel free to make changes if you want. Not sure about the type hints for data, currently the function accepts DataSet, DataTree and InferenceData. Support for InferenceData should be transitional as in ArviZ 1.0 we replace it with DataTree.

[amaloney]

I think this is a great start. There are some new plumbings in Python 3.13 that will make more complicated types easier to handle, but I think what you have now will work just fine.