Support the list type

[rlouf]

For instance to generate a list of integers:

model(prompt, list[int])

Linked to #1223

[Martins6]

hey @rlouf ,

the issued linked #1223 I believe to have solved via the creation of a BaseModel that encapsulated the specific schema into a list. So, just to be clear, this issue #1441 , wants a PR that automatically transforms schemas of type List[Any] into a valid schema such that it is going to create another schema that encapsulates that Any into a list, right?

In the #1223 , we would've List[Country] and then we would internally create CountryList that has the field of List[Country], is that correct?