dtypes with cmdstanpy

[OriolAbril]

We should take a look at how we handle dtypes in from_cmdstanpy (or directly on cmdstanpy). See teddygroves/figure_skating#1 for an example.

Note this is more of an issue candidate for now. I will try to play around a bit and see where things are going wrong, but I am posting anyways because 1) someone may already know the answer and I will not need to look into this and 2) maybe someone beats me into looking, I can't promise to look into this soon and we may want to fix this before the next release.

[ahartikainen]

io_cmdstan uses explicit dict

https://github.com/arviz-devs/arviz/blob/main/arviz/data/io_cmdstan.py

io_pystan access model_code to infer dtypes.

[ahartikainen]

CmdStanPy does not handle dtypes.