METADATA.toml versions redux#2 #6095

One practical problem with the current versioning scheme is that we can't correctly version the dataclasses stub. Current upstream version is 0.8. If we use 0.8 as version, the tests try to install dataclasses==0.8.*, which doesn't work. Similar problems would exist with calver or other exotic versioning schemes.

Currently, the tests try to install f"{distribution}=={version}.*. I would suggest that we allow standard Python version range specifiers in the version field and change most existing versions to use e.g. "5.3.*". The tests would then be changed to simply install f"{distribution}=={version}". This would give us more flexibility.