fix jina module not find bug (infiniflow#1779)

### What problem does this PR solve?

fix jina module not find bug

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

Co-authored-by: Zhedong Cen <cenzhedong2@126.com>

rag/llm/chat_model.py

@@ -28,7 +28,6 @@
 import json
 import requests
 import asyncio
-from rag.svr.jina_server import Prompt,Generation
 
 class Base(ABC):
     def __init__(self, key, model_name, base_url):
@@ -413,13 +412,15 @@ def __init__(self, key, model_name):
         self.client = Client(port=12345, protocol="grpc", asyncio=True)
 
     def _prepare_prompt(self, system, history, gen_conf):
+        from rag.svr.jina_server import Prompt,Generation
         if system:
             history.insert(0, {"role": "system", "content": system})
         if "max_tokens" in gen_conf:
             gen_conf["max_new_tokens"] = gen_conf.pop("max_tokens")
         return Prompt(message=history, gen_conf=gen_conf)
 
     def _stream_response(self, endpoint, prompt):
+        from rag.svr.jina_server import Prompt,Generation
         answer = ""
         try:
             res = self.client.stream_doc(