Desc

[ddudt]

Adds a utility function to generate a DESC input file from a near-axis solution.

The usage is very similar to the existing utility function for VMEC: Qsc.to_desc("input_filename"), with options to pass additional input parameters specific to DESC.

[ddudt]

Still need to add testing, similar to the testing used for VMEC. This will have to wait until DESC releases compatibility with fixed-current profile inputs.

[landreman]

Thanks! It would also be nice to have a unit test for ptolemy_identity(). (I'm away on vacation this week and next, Rogerio too, so we will be slow to respond for that time.)

[ddudt]

Fixed a few issues and started adding tests, including a unit test for ptolemy_identity(). The tests are failing because I try to import the desc module -- how do you want to handle this? Once that is resolved, we can also add tests to run the DESC equilibria as in to_vmec().

[rogeriojorge]

@ddudt I added an installation of DESC in CI to run all the tests there.
I also made the tests with VMEC and DESC optional using a flag "vmec_loaded" and "desc_loaded". This allows a user to run every test except the VMEC and DESC ones without an error at the end.