Refactor parsing of results files

[wtbarnes]

Fixes #86

This pull requests does a few things though is mainly focused on refactoring the parsing of the results files to try and simplify things:

• Move all file parsing logic to standalone functions in pydrad/parse/util.py that return astropy.table.QTable objects rather than arrays
• Properties on Strand are only dynamically generated if there are many of them or if they are unknown ahead of time (e.g. for the .ine files). Otherwise they are explicitly listed on Profile.
• Quantities are now pulled out of the resulting tables by column name rather than relying on indexing an array. This should be more robust.
• All results files are now optional except for the .amr files. If the .phy files are not read (or not present), the thermodynamic quantities are computed from the conserved quantities in the .amr files. See Function for calculating thermodynamic variables from conserved variables #86.

TODOs:

• Docstrings for quantities on Profile
• Create issue to track case where .amr file has an additional column for the electron mass density

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 44 lines in your changes missing coverage. Please review.

Project coverage is 71.50%. Comparing base (557e41a) to head (16cbbdd).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pydrad/parse/util.py	60.00%	18 Missing ⚠️
pydrad/parse/parse.py	87.71%	14 Missing ⚠️
pydrad/configure/configure.py	10.00%	9 Missing ⚠️
pydrad/visualize/animate.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #176      +/-   ##
==========================================
+ Coverage   70.41%   71.50%   +1.08%     
==========================================
  Files          11       13       +2     
  Lines         730      800      +70     
==========================================
+ Hits          514      572      +58     
- Misses        216      228      +12     

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[jwreep]

A few minor suggestions that you can ignore if you want. This looks otherwise fine to me! Thanks for putting this together.