adding Spheromak solutions

[mohawk811]

Description

This will provide some functions to solve for values relevant to Spheromak equilibria.

Motivation and context

Related issues

Closes #1995

[github-actions]

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[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (c5bafff) 98.21% compared to head (3cb920f) 98.21%.
Report is 56 commits behind head on main.

❗ Current head 3cb920f differs from pull request most recent head c3be2fd. Consider uploading reports for the commit c3be2fd to get more accurate results

Additional details and impacted files

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  Files          98       98           
  Lines        8568     8568           
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  Misses        153      153           

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[namurphy]

Here's the link that describes how to add an api_static file (and an example from #2068).

[namurphy]

Import & use the Bessel function from (I think) SciPy?

[namurphy]

Looks like SymPy has special functions for Bessel functions too.

[namurphy]

Suggested change

	Define Analytical solution for spheromak equilibria.
	Define Analytical solution for force-free spheromak equilibria.

[namurphy]

Suggested change

	class solution:
	class ForceFreeSpheromak:

...since I'm thinking we want to emphasize that it's force-free.