Numpy Version Issues

[M-Lampert]

Numpy released the version 2.0 recently. This currently leads to the following problem:

A module that was compiled using NumPy 1.x cannot be run in
NumPy 2.0.0 as it may crash. To support both 1.x and 2.x
versions of NumPy, modules must be compiled with NumPy 2.0.
Some module may need to rebuild instead e.g. with 'pybind11>=2.12'.

If you are a user of the module, the easiest solution will be to
downgrade to 'numpy<2' or try to upgrade the affected module.
We expect that some modules will need time to support NumPy 2.

I've set the numpy version to <2 for now (#191 ). I suggest we wait for now and bump up the version later when the problems are fixed. This issue should act as a reminder.