Expression evaluator should use the bit length set solver instead of forcing numerical expansion

[pavel-kirienko]

https://github.com/UAVCAN/pydsdl/blob/a1be9d99f88ce34d964d480ac5afeedaaa48a4d9/pydsdl/_data_type_builder.py#L184-L186

Originally posted by @thirtytwobits in #66 (comment)