Non-stellarator symmetric configurations in vmec_compute_geometry

[daringli]

Adds support for non-stellarator symmetric configurations in vmec_compute_geometry.

Also adds a relevant regression and sqrt(g) calculation test.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.99%. Comparing base (ab9096f) to head (2d0d7d3).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #575      +/-   ##
==========================================
+ Coverage   84.89%   84.99%   +0.09%     
==========================================
  Files          83       83              
  Lines       16291    16324      +33     
==========================================
+ Hits        13830    13874      +44     
+ Misses       2461     2450      -11     

Flag	Coverage Δ
unittests	84.99% <100.00%> (+0.09%)	⬆️

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[smiet]

Though I am not a great fan of this 500+ line function, the added functionality is great.

I did not go through the einsum-wrangling with a fine-toothed comb, but trust.

One comment about the test.

[smiet]

Given this comment, I gather that the precalc arrays are computed from the current state of the code. This makes them regression tests. Have you verified that these precalculated arrays are correct against physical properties of the input.basic_non_stellsym?

Could some test be added that is clearly non-stellarator-symmetric? Not sure of the interpretation of these arrays, but you could test whether the evaluation of quantities at +phi are not equal to that at minus phi.