IMAS support

[dgarnier]

Also fix errors with mypy and coverage. (Issue #16)

[codecov]

Codecov Report

Attention: Patch coverage is 95.17241% with 14 lines in your changes missing coverage. Please review.

Project coverage is 82.32%. Comparing base (dac4566) to head (41ad1e6).
Report is 14 commits behind head on main.

Files with missing lines	Patch %	Lines
python/dipoleq/imas.py	97.07%	5 Missing ⚠️
python/dipoleq/post_process.py	88.09%	5 Missing ⚠️
python/dipoleq/util.py	90.90%	3 Missing ⚠️
python/dipoleq/imas_dipole_extras.py	96.87%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #21      +/-   ##
==========================================
+ Coverage   75.75%   82.32%   +6.57%     
==========================================
  Files          11       14       +3     
  Lines        1031     1341     +310     
==========================================
+ Hits          781     1104     +323     
+ Misses        250      237      -13     

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[dgarnier]

I'm happy with this as an initial attempt. Not all derived quantities are in the IMAS yet, but the API looks good. Might mean a bump in subversion.