Improve handling of Python versioning strings

While working on https://github.com/dependabot/dependabot-core/pull/4928 Jake noticed that some of the ordering and parsing wasn't quite up to [PEP 440](https://peps.python.org/pep-0440)'s standards. In that PEP they have a list of version strings in order:

```
1.dev0
1.0.dev456
1.0a1
1.0a2.dev456
1.0a12.dev456
1.0a12
1.0b1.dev456
1.0b2
1.0b2.post345.dev456
1.0b2.post345
1.0rc1.dev456
1.0rc1
1.0
1.0+abc.5
1.0+abc.7
1.0+5
1.0.post456.dev34
1.0.post456
1.0.15
1.1.dev1
```

He tried those with our current setup and it failed in several ways. So this issue is to circle back and use the official regex and normalization logic to make that list ☝️ pass in a test.

Also we need to make sure that doing this doesn't break any current assumptions. One thought was since "Post releases" don't add anything substantial to the release we might want to ignore them completely otherwise Dependabot might annoy customers with unnecessary bumps.

I suspect we will see more bugs around Dependabot bumping versions incorrectly until we match the PEP standard.

Related:
* https://github.com/pypa/pip/issues/12012
* https://github.com/pypa/pip/issues/12063

Start with PEP 440's official version-string regex, normalization rules, and ordering example from the issue. Add a test covering the listed versions in order, then verify existing assumptions remain intact, including whether post releases should be ignored or retained.

Written by the indexing model from the issue text.