refactor pykoi into base, huggingface, rag, and rlhf

[garyjyzhang]

• refactor pykoi package into four sub packages
  • base: pip install pykoi. this contains openai model and chat
  • rag: pip install pykoi[rag]. this contains rag
  • huggingface: pip install pykoi[huggingface]. this contains huggingface moduels
  • rlhf: pip install pykoi[rlhf]. this contains rlhf features.

[CambioML]

LGTM!