def to_dict(self) -> at.PyTree[ArrayT]:
        """Convert the Observation to a nested dict."""
        result = dataclasses.asdict(self)
        result["image"] = result.pop("images")
        result["image_mask"] = result.pop("image_masks")
        return result
Convert the Observation to a nested dict.
policy/openpi/src/openpi/models/model.py