Support external python-types

[sheinbergon]

Changes

Fixes #423, #430

Adds a fallback for NotImplemented python_type errors, including test coverage using geoalchemy2

NOTICE: The test does not cover python 3.9, as geoalchemy2 dropped support for python 3.9 in its latest release and changed some other default behavior. As python 3.9 will soon reach EOL, I so no point in trying to cover it.

Checklist

If this is a user-facing code change, like a bugfix or a new feature, please ensure that
you've fulfilled the following conditions (where applicable):

• You've added tests (in tests/) which would fail without your patch
• You've added a new changelog entry (in CHANGES.rst).

If this is a trivial change, like a typo fix or a code reformatting, then you can ignore
these instructions.

Updating the changelog

If there are no entries after the last release, use **UNRELEASED** as the version.
If, say, your patch fixes issue #123, the entry should look like this:

- Fix big bad boo-boo in task groups
  (`#123 <https://github.com/agronholm/sqlacodegen/issues/123>`_; PR by @yourgithubaccount)

If there's no issue linked, just link to your pull request instead by updating the
changelog after you've created the PR.

[sheinbergon]

@agronholm I'm working to fix python 3.9 compatbility. As this regression is breaking, I'd like to release it as 3.1.1 as soon as we merge. That's why the CHANGES.rst already maps to 3.1.1

[coveralls]

coverage: 97.887% (+0.2%) from 97.671%
when pulling 87fe865 on sheinbergon:sheinbergon/not-implemented-python-type-handling
into 9c7477b on agronholm:master.

[sheinbergon]

@agronholm - The test does not cover python 3.9, as geoalchemy2 dropped support for python 3.9 in its latest release and changed some other default behavior. As python 3.9 will soon reach EOL, I see no point in trying to cover it.

[sheinbergon]

@agronholm can you push the 3.1.1 tag?

[agronholm]

I did that now. What happens if you try to push a tag?

[sheinbergon]

I don't think I can. I'll try in the next release 🙏

[agronholm]

You can try pushing a non-numeric tag, as those will not trigger the release process.