BUG: fix loading of AMReX datasets with ~ in the filename

[yut23]

PR Summary

One of our group members ran into this today when doing ds = CastroDataset('~/delta_ims/en_20/planar_plt02346'), with an error like:

yt/frontends/boxlib/data_structures.py", line 1116, in _parse_parameter_file
    jobinfo_filename = os.path.join(self.output_dir, self.cparam_filename)
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen posixpath>", line 90, in join
  File "<frozen genericpath>", line 164, in _check_arg_types
TypeError: join() argument must be str, bytes, or os.PathLike object, not 'NoneType'

self._lookup_cparam_filepath() was being passed the version of output_dir before having the tilde expanded, and was returning None as ./~/ doesn't exist.

I'm not sure how to add a test for this.

PR Checklist

• Adds a test for any bugs fixed. Adds tests for new features.

[neutrinoceros]

The patch is simple enough that I don't think we need a test for it. But I think this class should reuse code from its parent instead of reimplementing identical yet buggy logic.

[neutrinoceros]

It should be possible to use self.directory instead provided the parent class' __init__ is called first. Can you try that ?

[yut23]

Unfortunately that doesn't work: Dataset.__init__() calls self._parse_parameter_file(), which needs self.cparam_filename to be set beforehand.

[neutrinoceros]

fair enough !