Setuptools version 69 requires pyproject.toml

[SimonMaenaut]

As noted in the setuptools documentation setup_requires in setup.py was deprecated and a pyproject.toml file is required.

In addition to

cpnest/setup.py

Line 73 in 249c0e2

setup_requires=['numpy', 'cython', 'setuptools_scm'],

and

cpnest/setup.cfg

Lines 4 to 6 in 249c0e2

	[options]
	setup_requires =
	setuptools_scm numpy cython

a new pyproject.toml file should be added:

[build-system]
requires = ["setuptools_scm", "numpy", "cython"]

This made it possible to install cpnest on python 3.12 with setuptools 69.5.1 and should be compatible with older versions.

[johnveitch]

Closed by #90