use importlib instead of imp module on Python3.12

[yuzibo]

Hi,

I just google some links about imp was deprecated on python3.12. On Debian, we have one ftbfs below:

    cmd_obj.ensure_finalized()
  File "/usr/lib/python3/dist-packages/setuptools/_distutils/cmd.py", line 111, in ensure_finalized
    self.finalize_options()
  File "/usr/lib/python3/dist-packages/setuptools/command/egg_info.py", line 225, in finalize_options
    parsed_version = packaging.version.Version(self.egg_version)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/setuptools/_vendor/packaging/version.py", line 198, in __init__
    raise InvalidVersion(f"Invalid version: '{version}'")
setuptools.extern.packaging.version.InvalidVersion: Invalid version: 'unknown'
E: pybuild pybuild:389: build: plugin distutils failed with: exit code=1: /usr/bin/python3 setup.py build 

But the back track was unclear, the question is raised from imp imported, so I purpose one patch:

--- a/pycorrfit/_version.py
+++ b/pycorrfit/_version.py
@@ -12,7 +12,7 @@
 # Put the entire script into a `True` statement and add the hint
 # `pragma: no cover` to ignore code coverage here.
 if True:  # pragma: no cover
-    import imp
+    import importlib
     import os
     from os.path import abspath, basename, dirname, join
     import subprocess

It seems it works on my local build. Could you have a look at this?
Thanks.

[paulmueller]

Hi @yuzibo
I currently do not have time to work on PyCorrFit, but I would be happy to merge a PR. Generally, it would probably be best to migrate to pyproject.toml + setuptools_scm for managing versioning.