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