feat: 1. replace black with ruff for fomatting and sort import (#489)

2. use tavily from`langchain-tavily` rather than the older one from `langchain-community`

Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

src/rag/retriever.py

@@ -2,6 +2,7 @@
 # SPDX-License-Identifier: MIT
 
 import abc
+
 from pydantic import BaseModel, Field