Automatically generate internal type hint overloads

[willbakst]

Originally proposed by @teamdandelion in #896 discussion

In preparation for the v2.0 release, we should work on auto-generating the type hint overloads for v1.x.

For example, the llm.override method has insane type overloads that overload for every provider. If we want to do this for every model in the future, we'll need a way to auto-generate these to avoid massive headaches in the furture.