Fix compatibility with numpy 2

[MartinCapraro]

This PR simply replaces the usage of the deprecated numpy types np.float_ and np.complex_ with np.float64 and np.complex128. This seems to be sufficient to obtain compatibility with numpy 2.0.1.

[MartinCapraro]

I should perhaps add some detail to explain how I confirmed this works:

I forked the repo, and removed the restriction in setup.py that numpy<2 is required for installation. I then installed the fork in a new virtualenv with pip install . --use-pep517. I then attempted to run a simple script from the tutorial, fixing the errors as they came up, until the script ran successfully.

The tests also mostly passed. There are two that fail, with the id cluster_10^-4 but they also fail when I cloned the master branch of the main repo. Looking at the github build/test logs (e.g. https://github.com/rparini/cxroots/actions/runs/10121727774/job/27993000890) I actually think they may be excluded from the test action somehow? I don't know if that's intentional.

[rparini]

@MartinCapraro thanks for this!

There are two that fail, with the id cluster_10^-4 but they also fail when I cloned the master branch of the main repo. Looking at the github build/test logs (e.g. https://github.com/rparini/cxroots/actions/runs/10121727774/job/27993000890) I actually think they may be excluded from the test action somehow? I don't know if that's intentional

Yes that is a very slow test so I've configured CI to skip it. My expectation is it should pass when run locally so I'll have a look at that sometime. I think it doesn't need to hold up this PR though.