Pin NumPy below new major release (2.0.0) until dependencies are compatible

The impending major NumPy release (2.0.0) will apparently introduce a number of issues in, at the very least, our dependencies, if not our own code. I'm capping NumPy versions below this so that we don't inadvertently break the code when the new release is made public.

From there we can assess dependency compatibility and update as needed.