Build using NumPy 2.0

[peterjc]

Quoting https://github.com/numpy/numpy/blob/main/doc/source/dev/depending_on_numpy.rst under build-time dependencies:

Before NumPy 1.25, the NumPy C-API was not backwards compatible. This means that when compiling with a NumPy version earlier than 1.25 you have to compile with the oldest version you wish to support. This can be done by using oldest-supported-numpy. Please see the NumPy 1.24 documentation.

We have been building against the older possible NumPy v1 as per the opening paragraph quoted.

However, according to the numpy mailing lists etc, I understand that once NumPy v2 is out, we should build or wheels using that in order to be compatible with both NumPy 1.x and 2.x. The documentation at the link above will likely be updated soon...