Create and check attrs at init

[wd60622]

Following #867, this would create the attrs which would be store on the InferenceData at initializiation rather than only after fit or sample_prior_predictive. This would be faster feedback for new models if the attrs are insufficient.

There are some difficulties with this approach as the attrs contains the id which depends on the model_config so any modifications to the model_config will have to happen before the id is created.