I noticed that the file interface.py currently contains two classes: Keepa and AsyncKeepa.

Would you be open to me splitting this file into two separate files (e.g., keepa_sync.py and keepa_async.py) to improve clarity and maintainability?

One more thing, I don't think using the name 'interface' for the implementation of the two classes is fine. Can we use some real interfaces for the classes, like keepa_sync.ipy, keepa_async.ipy?

Let me know if you’re okay with this change — I can open a PR for it.

Thanks!