Explore generalisability of the generator functions

[seabbs]

          I can see that the `log_lik` one has the name in. I don't think these functions will work by default with e.g. the marginal model. Is the point that they'll be modified then? Some question about whether for the time being for consistency they should be named `latent` given that they don't work with the marginal model as is (and the marginal model doesn't exist yet)?

Originally posted by @athowes in #459 (comment)

Focus on if they can be used across a range of models (or what is needed to make this be the case). If they can be but only a subset explore how to make this clear to users