arviz v0.11.4 has, according to its requirements.txt, a dependency on
typing-extensions < 4. Currently, only typing-extensions v.4.0.1 are
available in nixpkgs, while the above version constraint seems
unnecessary, see this arviz PR: https://github.com/arviz-devs/arviz/pull/1948/files.
This also activates tests that use zarr and to which changes are made
in above PR. I thought those changes might be related to
unconstraining the typing-extensions version, but looks like they are not.
The tests in this version of arviz require an older version of
TensorFlow Probability than the one packaged in this PR.
This also fixes a few missing dependencies.
