Ensure all models have temperature and top_k control

[philwinder]

In many cases you want to alter the model to produce more consistent results, especially when you're trying to figure out what prompts work.

Currently there's no temperature/top_k setting at all, so it's using whatever default the model has.

First step would be to at least set a default in the code, so we can see it getting set. The second step would be to pass that back through to all the top level APIs.