first step to support numpy 2.0

call np.import_array https://github.com/cython/cython/wiki/tutorials-numpy#c-api-initialization

to avoid the following error:

ultranest/mlfriends.pyx:1: in init ultranest.mlfriends
    # cython: language_level=3,annotate=True,profile=True,fast_fail=True,warning_errors=True
E   ImportError: numpy.core.multiarray failed to import (auto-generated because you didn't call 'numpy.import_array()' after cimporting numpy; use '<void>numpy._import_array' to disable if you are certain you don't need it).
------------------------------- Captured stderr --------------------------------

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.

also see
https://numpy.org/doc/stable//dev/depending_on_numpy.html#numpy-2-abi-handling
https://numpy.org/doc/stable//numpy_2_0_migration_guide.html

ultranest/mlfriends.pyx

@@ -16,6 +16,7 @@ Includes
 
 import numpy as np
 cimport numpy as np
+np.import_array()
 from numpy import pi
 cimport cython
 from cython.cimports.libc.math import sqrt

ultranest/stepfuncs.pyx

@@ -7,6 +7,7 @@ Efficient helper functions for vectorized step-samplers
 
 import numpy as np
 cimport numpy as np
+np.import_array()
 from numpy import nan as np_nan
 cimport cython
 from cython.parallel import prange