numpy 2 breaking changes

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Hi Malcolm / anyone else finally upgrading their system

FYI for numpy 2.0 there seems to be only one minor edit needed, np.infty is now np.inf. Aside from adding the parallel definitions in fields.cpp only need to address line 435 in fields.pyx. I think np.inf exists in numpy 1.26 as well so possibly worth it to just swap it completely (?)