BLD: unvendor meson-python

[rgommers]

The meson-python 0.15.0 release added the ability to configure a custom meson in pyproject.toml. So there's no longer a need for us to vendor it.

[rgommers]

Python 3.12 failures:

  meson.build:40:22: ERROR: <PythonExternalProgram 'python3' -> ['/opt/hostedtoolcache/Python/3.12.0/x64/bin/python']> is not a valid python or it is missing distutils

The vendored Meson needs an update so that we're getting the fixes in Meson 1.2.3 to avoid distutils/setuptools completely.

[rgommers]

Almost victory - a single test error left in the "without optimizations" job of linux_simd.yml:

  ----------------------------- Captured stderr call -----------------------------
  Traceback (most recent call last):
    File "/tmp/pytest-of-runner/pytest-0/test_limited_api0/limited_api/setup.py", line 6, in <module>
      from setuptools import setup, Extension
  ModuleNotFoundError: No module named 'setuptools'
  =========================== short test summary info ============================
  FAILED numpy/_core/tests/test_limited_api.py::test_limited_api - subprocess.CalledProcessError: Command '['/opt/hostedtoolcache/Python/3.12.0/x64/bin/python', 'setup.py', 'build', 'install', '--prefix', '/tmp/pytest-of-runner/pytest-0/test_limited_api0/installdir', '--single-version-externally-managed', '--record', '/tmp/pytest-of-runner/pytest-0/test_limited_api0/tmp_install_log.txt']' returned non-zero exit status 1.

That's because on 3.12 we no longer install setuptools as a build dependency, and it's needed as a test dependency there. Should be fixed by the last commit.

[rgommers]

Victory! This is ready to merge.

[charris]

Thanks Ralf.