GX wrapper with ExternalObjective

[YigitElma]

An updated version of the GX wrapper with ExternalObjective similar to Terpsichore one.

Summary of the wrapper:

• Takes in DESC equilibrium object
• Computes field line quantities on chosen alpha
• Writes the GX geometry input file (updates the main GX input file to point to this file)
• Calls GX in a subprocess (user can pass custom CLI commands)
• Reads the GX output
• Returns the averaged heat flux

Things to consider:

• compute_gx_geometry function can be moved to a different location in DESC and can be shared with Add ITG turbulence proxy and neural network objectives #2080

Note: I used Patrick's original PR (#1001), Byoungchan's new PR (#2080) and GX's internal DESC geometry creator as reference for the implementation.

#1001 can be closed after this

[github-actions]

Memory benchmark result

|               Test Name                |      %Δ      |    Master (MB)     |      PR (MB)       |    Δ (MB)    |    Time PR (s)     |  Time Master (s)   |
| -------------------------------------- | ------------ | ------------------ | ------------------ | ------------ | ------------------ | ------------------ |
  test_objective_jac_w7x                 |    1.33 %    |     4.191e+03      |     4.247e+03      |    55.72     |       43.27        |       39.76        |
  test_proximal_jac_w7x_with_eq_update   |   -0.66 %    |     6.534e+03      |     6.491e+03      |    -43.42    |       158.74       |       162.19       |
  test_proximal_freeb_jac                |   -0.27 %    |     1.340e+04      |     1.337e+04      |    -35.56    |       88.45        |       86.83        |
  test_proximal_freeb_jac_blocked        |   -0.66 %    |     7.743e+03      |     7.692e+03      |    -51.18    |       77.70        |       77.00        |
  test_proximal_freeb_jac_batched        |    0.14 %    |     7.673e+03      |     7.684e+03      |    10.62     |       76.69        |       78.22        |
  test_proximal_jac_ripple               |   -0.71 %    |     3.653e+03      |     3.627e+03      |    -25.92    |       63.28        |       62.77        |
  test_proximal_jac_ripple_bounce1d      |   -3.81 %    |     3.890e+03      |     3.742e+03      |   -148.40    |       77.67        |       77.04        |
  test_eq_solve                          |   -0.22 %    |     2.221e+03      |     2.216e+03      |    -4.89     |       98.68        |       97.03        |

For the memory plots, go to the summary of Memory Benchmarks workflow and download the artifact.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.72%. Comparing base (f8c0ec0) to head (b59a15b).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2150      +/-   ##
==========================================
+ Coverage   94.48%   95.72%   +1.24%     
==========================================
  Files         102      101       -1     
  Lines       28721    28351     -370     
==========================================
+ Hits        27137    27139       +2     
+ Misses       1584     1212     -372     

see 2 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.