SQLModel support & tests#363

Add support for models configured via https://github.com/fastapi/sqlmodel As of current `SQLModel`/`SQLAlchemy`/`SQLAlchemy-Continuum` API, there is no need to depend on `SQLModel` to support it, as only change needed is to make `SQLAlchemy-Continuum` to pull `SQLAlchemy` class registry from different attribute for `SQLModel` derived models as compared to pure `SQLAlchemy` defined ones. The `base_classes` parameter for versioned models does not work with `SQLModel`, `pydantic` metaclass magic fails for version model classes created with `base_classes` passed, because they are lacking `__module__` attribute somehow, leading to `AttributeError` inside pydantic meta methods. Since I do not use `base_classes` in my projects, I decided not to put effort to support it in this patch, but future support might need changes in either `SQLModel` or `pydantic`. Otherwise, most of stuff seem to work well, ported CRUD and relationships tests to run with `SQLModel` defined models as part of this PR. I'd like to say thanks to https://github.com/AlePiccin who suggested the idea behind this PR implementation here: https://github.com/kvesteri/sqlalchemy-continuum/issues/271#issuecomment-2521189305