Builder return value doesn't have to_python

[mccalluc]

In many instances, the the builder return is a raw dict or list... It doesn't do what we need:

FAILED test/test_builders.py::test_entity_to_vitessce_conf[StitchedCytokitSPRMViewConfBuilder/04e7385339167e541ad42a2636e18398-entity.json] - AttributeError: 'dict' object has no attribute 'to_python'
FAILED test/test_builders.py::test_entity_to_vitessce_conf[SeqFISHViewConfBuilder/fake-entity.json] - AttributeError: 'list' object has no attribute 'to_python'
FAILED test/test_builders.py::test_entity_to_vitessce_conf[IMSViewConfBuilder/fake-entity.json] - AttributeError: 'dict' object has no attribute 'to_python'
FAILED test/test_builders.py::test_entity_to_vitessce_conf[MultiImageSPRMAnndataViewConfBuilder/fake-entity.json] - AttributeError: 'list' object has no attribute 'to_python'
FAILED test/test_builders.py::test_entity_to_vitessce_conf[TiledSPRMViewConfBuilder/with-cells-entity.json] - AttributeError: 'list' object has no attribute 'to_python'
FAILED test/test_builders.py::test_entity_to_vitessce_conf[TiledSPRMViewConfBuilder/no-cells-entity.json] - AttributeError: 'list' object has no attribute 'to_python'
FAILED test/test_builders.py::test_entity_to_vitessce_conf[ImagePyramidViewConfBuilder/fake-entity.json] - AttributeError: 'dict' object has no attribute 'to_python'