Fix errors detected by Ruff (#3918)

### What problem does this PR solve?

Fix errors detected by Ruff

### Type of change

- [x] Refactoring

rag/llm/sequence2txt_model.py

@@ -15,12 +15,9 @@
 #
 import requests
 from openai.lib.azure import AzureOpenAI
-from zhipuai import ZhipuAI
 import io
 from abc import ABC
-from ollama import Client
 from openai import OpenAI
-import os
 import json
 from rag.utils import num_tokens_from_string
 import base64
@@ -49,7 +46,8 @@ class Base(ABC):
 
 class GPTSeq2txt(Base):
     def __init__(self, key, model_name="whisper-1", base_url="https://api.openai.com/v1"):
-        if not base_url: base_url = "https://api.openai.com/v1"
+        if not base_url:
+            base_url = "https://api.openai.com/v1"
         self.client = OpenAI(api_key=key, base_url=base_url)
         self.model_name = model_name