refactor: remove unused response normalizer module

- Delete unused ResponseNormalizer class and its initialization logic
- Remove response_normalizer and enable_response_normalization parameters from handlers
- Simplify chat adapter base initialization by removing normalizer setup
- Clean up unused imports in handler modules

src/api/handlers/gemini/handler.py

@@ -148,17 +148,6 @@ class GeminiChatHandler(ChatHandlerBase):
 
         Returns:
             规范化后的响应
-
-        TODO: 如果需要，实现响应规范化逻辑
         """
-        # 可选：使用 response_normalizer 进行规范化
-        # if (
-        #     self.response_normalizer
-        #     and self.response_normalizer.should_normalize(response)
-        # ):
-        #     return self.response_normalizer.normalize_gemini_response(
-        #         response_data=response,
-        #         request_id=self.request_id,
-        #         strict=False,
-        #     )
+        # 作为中转站，直接透传响应，不做标准化处理
         return response