refactor: 重构Gemini和OpenAI聊天服务以支持工具和安全设置

- 将 `_build_payload`、`_build_tools`、`_get_safety_settings` 和 `_has_image_parts` 函数从 `OpenAIChatService` 和 `GeminiChatService` 类中提取为独立的函数。
- 将 `_handle_stream_response` 和 `_handle_normal_response` 函数从 `GeminiResponseHandler` 和 `OpenAIResponseHandler` 类中提取为独立的函数。
- 将 `_extract_text` 函数从 `OpenAIResponseHandler` 类中提取为独立的函数, 并在 `GeminiResponseHandler` 中复用。
- 将 `_convert_image` 函数从 `OpenAIMessageConverter` 类中提取为独立的函数。
- 优化 `OpenAIChatService` 和 `GeminiChatService` 中的代码结构, 使其更清晰。
- 优化 `app/api/openai_routes.py` 和 `app/api/gemini_routes.py` 中的路由函数, 移除不必要的参数。

app/services/chat/api_client.py

@@ -4,24 +4,26 @@ from typing import Dict, Any, AsyncGenerator
 import httpx
 from abc import ABC, abstractmethod
 
+
 class ApiClient(ABC):
     """API客户端基类"""
-    
+
     @abstractmethod
     async def generate_content(self, payload: Dict[str, Any], model: str, api_key: str) -> Dict[str, Any]:
         pass
-        
+
     @abstractmethod
     async def stream_generate_content(self, payload: Dict[str, Any], model: str, api_key: str) -> AsyncGenerator[str, None]:
         pass
 
+
 class GeminiApiClient(ApiClient):
     """Gemini API客户端"""
-    
+
     def __init__(self, base_url: str, timeout: int = 300):
         self.base_url = base_url
         self.timeout = timeout
-        
+
     def generate_content(self, payload: Dict[str, Any], model: str, api_key: str) -> Dict[str, Any]:
         timeout = httpx.Timeout(self.timeout, read=self.timeout)
         if model.endswith("-search"):
@@ -33,14 +35,14 @@ class GeminiApiClient(ApiClient):
                 error_content = response.text
                 raise Exception(f"API call failed with status code {response.status_code}, {error_content}")
             return response.json()
-            
+
     async def stream_generate_content(self, payload: Dict[str, Any], model: str, api_key: str) -> AsyncGenerator[str, None]:
         timeout = httpx.Timeout(self.timeout, read=self.timeout)
         if model.endswith("-search"):
             model = model[:-7]
         async with httpx.AsyncClient(timeout=timeout) as client:
             url = f"{self.base_url}/models/{model}:streamGenerateContent?alt=sse&key={api_key}"
-            async with client.stream("POST", url, json=payload) as response:
+            async with client.stream(method="POST", url=url, json=payload) as response:
                 if response.status_code != 200:
                     error_content = await response.aread()
                     error_msg = error_content.decode("utf-8")