Refactor web search plugin and clean up code

Refactored the web search plugin by removing the old Bing search implementation and reorganizing the plugin structure. Introduced modular search engine classes under 'web_search_tool/engines' and utility tools under 'web_search_tool/tools' and 'web_search_tool/utils'. Updated references and initialization logic to support multiple search engines and improved maintainability. Also performed minor code cleanups and replaced 'except ...: pass' with 'except ...: ...' for brevity.

src/chat/utils/prompt_builder.py

@@ -70,8 +70,8 @@ class PromptContext:
                     # 如果reset失败，尝试直接设置
                     try:
                         self._current_context = previous_context
-                    except Exception:
-                        pass  # 静默忽略恢复失败
+                    except Exception: ...
+                    # 静默忽略恢复失败
 
     async def get_prompt_async(self, name: str) -> Optional["Prompt"]:
         """异步获取当前作用域中的提示模板"""