Explicitly set numba config for each jit function

[leouieda]

Using parallel=True on the Green's function was raising a warning
because there is nothing to parallelize. Set arguments individually to
avoid this. Add missing numba.prange to Spline Jacobian calculation to
actually run it in parallel.

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst and verde/__init__.py.
• Write detailed docstrings for all functions/classes/methods.
• If adding new functionality, add an example to the docstring, gallery, and/or tutorials.

[leouieda]

I think #222 might fix some of these failures so waiting on that.

[leouieda]

For some reason, the Dask related tests and docs hang in CI when using numba. I can't reproduce locally so it's hard to pin point. Will try removing the parallel arg from numba to see if that's the problem.

[leouieda]

Alright, using the numpy engine with the dask tests seems to work. Strange because the tutorials work.

[leouieda]

Merging this in since things seem to be working.