DEP: refactored out runtime dependency on setuptools

[neutrinoceros]

Yesterday we ran into some issues with the latest version of setuptools at astropy (see this issue for context).
In summary, what happened is that setuptools 71 brought in a couple runtime side effects, resulting in some confusing error messages.
My analysis showed that setuptools is only present in the runtime environment that astropy runs tests with because it's brought in by this package, which only requires it for a single line of code, so I refactored it using standard lib importlib.metadata + packagaging (which is already a runtime dependency here), eliminating setuptools as a runtime dependency, which down the road eliminates a source of instabilitly for any package that relies on pytest-doctestplus.

In case it's not clear (it wasn't to me), note that pkg_resources is really part of setuptools and not included in the standard library.

[pllim]

Why is it still needed in test?

[neutrinoceros]

That's because some tests (e.g. tests/test_doctestplus.py::test_ufunc) include an entire setup.py script that requires setuptools

[pllim]

Just to make sure the failures are related, I reran a previously successful build from 3 days ago: https://github.com/scientific-python/pytest-doctestplus/actions/runs/9950476771

Update: main is green, so failures probably related.

[pllim]

Since this removes a required dependency, might need a change log as well.

[neutrinoceros]

yup; failures are related, I'll have a look.

[neutrinoceros]

Failures are specifically hit with pre-releases versions of pytest. I'm going to force push the fix. For ease of read, here it is

diff --git a/pytest_doctestplus/utils.py b/pytest_doctestplus/utils.py
index f30e1f5..8a6df5c 100644
--- a/pytest_doctestplus/utils.py
+++ b/pytest_doctestplus/utils.py
@@ -20,7 +20,7 @@ class ModuleChecker:
         except Exception:
             return None
         else:
-            if reqs.specifier.contains(dist_meta.version):
+            if reqs.specifier.contains(dist_meta.version, prereleases=True):
                 return dist_meta
             else:
                 return None

[pllim]

LGTM. Thanks!

[pllim]

Looks like Squash & Merge not enabled here, so thanks for squashing!