Refactor coil tests to use `pytest.mark.parametrize` which treats it as different tests rather than 1 big one so easier to debug and run specific ones in case of failure.

[dpanici]

might be able to refactor this to use pytest.mark.parametrize which treats it as different tests rather than 1 big one so easier to debug and run specific ones in case of failure.

_Originally posted by @f0uriest in https://github.com/PlasmaControl/DESC/pull/1099#discussion_r1667216952_

[dpanici]

https://stackoverflow.com/questions/42014484/pytest-using-fixtures-as-arguments-in-parametrize could be helpful, I found it slightly annoying to figure out though since we need to add some logic to load the coilset only for certain parametrizations and not others