add numpy 2 support

[MuellerSeb]

Closes: #337 #345

Numpy 2.0.0rc1 was released: https://pypi.org/project/numpy/2.0.0c1 and is officially usable to build extensions.

• numpy 2.0.0rc1 for building extensions (for Python 3.9 and above)
• check multiple numpy and scipy versions in CI
• fixed minimal versions for numpy
• use np.asarray everywhere with np.atleast_(n)d
• fix long/longlong integer issue in cython on windows by always using 64bit integers

Additional doc fixes

• build docs with latest sphinx version
• require pyvista 0.40 at least

32bit builds were removed with this PR. I think we can happily drop that.

[MuellerSeb]

• Building with numpy 2 works :tada:
• Running tests with numpy 2 fails :sob:

A lot of the tests fail because of emcee and this issue: https://github.com/dfm/emcee/issues/509

Other errors have a problem with these lines in estimator.pyx:

    cdef long[:, :] counts = np.zeros((d_max, len(bin_edges)-1), dtype=long)
    cdef long[:] counts = np.zeros(len(bin_edges)-1, dtype=long)
    cdef long[:] counts = np.zeros(k_max, dtype=long)
    cdef long[:] counts = np.zeros(k_max, dtype=long)

and raise

E   ValueError: Buffer dtype mismatch, expected 'long' but got 'long long'

This only occurs on windows and is related to this: https://numpy.org/devdocs/numpy_2_0_migration_guide.html#windows-default-integer

One other category of errors is:

If using `np.array(obj, copy=False)` replace it with `np.asarray(obj)` to allow a copy when needed (no behavior change in NumPy 1.x).

np.array(..., copy=False) is used in krige/base.py, 3 times in variogram/variogram.py and 3 times in tools/geometric.py

In order to mimic the ndmin=... feature, we could replace these with e.g.:

pos = np.atleast_2d(np.asarray(pos, dtype=np.double))

[MuellerSeb]

All issues fixed. Only remaining issues should be solved upstream in emcee with: https://github.com/dfm/emcee/pull/510