Switch from versioneer to pypa/setuptools_scm

[jcfr]

Would it be a good idea to move to pypa/setuptools_scm? It has nice tooling for this sort of thing; the manual versioner script doesn't have the nice overrides.

Originally posted by @henryiii in https://github.com/scikit-build/cmake-python-distributions/issues/141#issuecomment-845240054

---

We are currently versioneer, which problem would setuptools_scm address ?

Two problems. One is we have a lot of custom code (including versioneer.py and various workarounds), while setuptools_scm simply is a PyPI package. Second, with setuptools_scm, there are environment variable overrides (specifically, I needed SETUPTOOLS_SCM_PRETEND_VERSION) that can be used for emergency operations like this one. Also, it's a PyPA standard package instead of custom code.

Originally posted by @henryiii in https://github.com/scikit-build/cmake-python-distributions/issues/141#issuecomment-845254006

[henryiii]

Was just about to open this. :)

[mayeut]

I tried moving to pypa/setuptools_scm but something went wrong with the MANIFEST for sdist at least (nox failing there). It might be related to https://github.com/scikit-build/scikit-build/pull/402 (or not), needs further investigation.