Bring back AI models as const

[demosjarco]

In commit 7f3789c, modelMappings was removed and replaced by creating union types directly in the argument in the run() overloads. This removes the ability to get the models available at runtime.

Also putting the model names directly inline to each overload makes it difficult to retrieve the models for a task type outside of the run() method vs. externalizing each one individually (or as part of a namespace or other grouping method).