Switch to using freeqdsk to read geqdsk files

[ZedThree]

No description provided.

[dschwoerer]

I am not a fan of new dependencies, I doubt that freeqdsk is packaged for fedora, so updating zoidberg will require packaging that as well, and its dependency fortranformat.

So I am wondering - what are the advantages of freeqdsk?

[ZedThree]

freeqdsk is becoming the community standard package for reading geqdsk files, and I'm pushing to remove custom implementations in favour of a single, maintained package.

It also has more features than other implementations, including aeqdsk and peqdsk formats, support for COCOS numbers != 1, some customisation of the header format.

[dschwoerer]

Seems like worthy goals 👍
The dependency tree seems manageable.
Only question is whether there are enough tokamak users that justify to set this as a hard dependency.
We could maybe also add an extra tokamak = freeqdsk section to options.extras_require?