First: thank you for this PR.
Unfortunately I no longer have any hardware to test this code since I sold my house several years ago.
I'm not much of a Python expert and learned about mixins from your code, thanks!
Yes, there is no consistency in tabs vs spaces, it's a mess. I will clean it up to meet PEP 8 after your PR has been merged.
The one thing that puzzles me about your PR is the import statements. Do you really need to specify the full path (python.mixins.xxx)? I really don't like the "python" in the front since it suggests that this is a module that belongs to the python language. @pfrommerd put something in the Readme that says that the import statements should not include "python" at the beginning. I think the import also works without the "python." in front. At least I can instantiate an object and invoke some methods on it.

I actually spent a long time trying to figure out the imports. I've never worked on a Jython project before. I usually have a virtualenv in my past projects. The imports only seemed to work with the python workspace. We could eliminate it if we put everything in the same folder. It looks like the content of the folder is currently pretty mixed anyways.

Or, I could submit another pull request that just copies and pastes the relevant functions which is a little redundant, but consistent.

I'm a bit puzzled by the fact that you need the "python." since all the other imports work without it (using openjdk 11.0.19 python 3.10.6 on Ubuntu 22.04). Could you please double check that you cannot do without the "python."? For me your class works with or without the "python." prefix on the import.
If the sub directories are the cause of the problem, then I'd rather you eliminate them as you suggested. I may be guilty of code duplication myself but I generally avoid it.