feat: TanStack AI providers

[jakobhoeg]

This is a very ambitious feature request:
Build 3 new providers (adapters) as npm packages for TanStack AI SDK to make this repository the one point entry for built-in/in-browser model providers/adapters.

Mentioned as a feature request here: TanStack/ai#145

[jakobhoeg]

This is definitely do-able with the ConnectionAdapter interface. Not sure how limited it is, but I currently have a working (wip) implementation for Prompt API:

tanstack.mp4