Infer dtypes for all Stan interfaces

[ahartikainen]

Description

closes #1630

Checklist

• Follows official PR format
• Includes a sample plot to visually illustrate the changes (only for plot-related functions)
• New features are properly documented (with an example if appropriate)?
• Includes new or updated tests to cover the new feature
• Code style correct (follows pylint and black guidelines)
• Changes are listed in changelog

Infer dtypes from model code (all interfaces) or use user given dictionary (cmdstanpy, cmdstan).

[OriolAbril]

Looks good, are you planning on adding tests? Maybe a test directly on infer_stan_dtypes is enough. We can always create an issue to see if it gets done

[ahartikainen]

Yes. (I have not tested these yet)

[codecov]

Codecov Report

Merging #1632 (679cd3a) into main (60988ff) will decrease coverage by 0.04%.
The diff coverage is 89.69%.

@@            Coverage Diff             @@
##             main    #1632      +/-   ##
==========================================
- Coverage   90.90%   90.86%   -0.05%     
==========================================
  Files         108      108              
  Lines       11762    11818      +56     
==========================================
+ Hits        10692    10738      +46     
- Misses       1070     1080      +10     

Impacted Files	Coverage Δ
arviz/data/io_cmdstan.py	89.80% <45.45%> (-1.15%)	⬇️
arviz/data/io_cmdstanpy.py	95.43% <84.61%> (-1.07%)	⬇️
arviz/data/base.py	98.21% <100.00%> (+0.34%)	⬆️
arviz/data/io_pystan.py	96.08% <100.00%> (-0.01%)	⬇️

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[ahartikainen]

I also added dtypes option for from_pystan, so if users have complicated stan file, they still have possibility to define correct dtypes.

[OriolAbril]

Not sure I did a very good job with the changelog, either way, feel free to merge whenever