BaseAS interface

[orperel]

This pull request adds the BaseAS abstract, to unify the upcoming acceleration structures under a single interface.

Notably raymarch / raytrace / query now return dataclasses of results. This is desired because:

1. It allows to easily handle and pass around the various return values from these functions
2. In case some raymarch ops return other output formats in the future, we could more easily enforce it by querying the dataclass return type