PEP 420 native namespaces

Now that Plone 6.2 is released, all python distributions from the plone and collective namespaces should move to [python native namespaces](https://6.docs.plone.org/developer-guide/native-namespace.html).

Despite native namespaces being a new feature of Python 3.3, we have a problem with `collective.exportimport` as its purpose is to help move very old code bases, some still on Python 2.7.

Suggestions on how to handle this with as less friction as possible? 🤞🏾

Start with the linked Plone native-namespace guide and review collective.exportimport's current Python 2.7 compatibility requirements. Determine how the package can adopt native namespaces without breaking legacy consumers; done means a documented migration decision and compatible release plan.

Written by the indexing model from the issue text.