fix: 修复 GeneratorExit 和 Task destroyed 警告

问题: 协程被取消/销毁时，finally 块中的异步操作触发 GeneratorExit
原因: GeneratorExit 是 BaseException 子类，不会被 Exception 捕获

修复内容:
- server.py handle(): 捕获 CancelledError + GeneratorExit
- server.py _tunnel(): 被取消时不执行 _record_stats() 异步操作
- instances.py _accept_connection(): 添加异常处理和 writer 关闭
- 所有取消场景都静默处理（不抛异常/不记录错误日志）

engine/instances.py

@@ -114,14 +114,23 @@ class Socks5Server:
         )
 
     async def _accept_connection(self, reader, writer):
-        with self._lock:
-            self._active_connections += 1
-        handler = ConnectionHandler(
-            reader, writer, self.config, self.user_service,
-            flask_app=self.flask_app,
-            on_close_cb=self._on_connection_close
-        )
-        await handler.handle()
+        try:
+            with self._lock:
+                self._active_connections += 1
+            handler = ConnectionHandler(
+                reader, writer, self.config, self.user_service,
+                flask_app=self.flask_app,
+                on_close_cb=self._on_connection_close
+            )
+            await handler.handle()
+        except (asyncio.CancelledError, GeneratorExit):
+            # 服务器关闭时正常取消，不记录错误
+            pass
+        finally:
+            try:
+                writer.close()
+            except Exception:
+                pass
 
     def _on_connection_close(self, handler):
         with self._lock:

engine/server.py

@@ -104,6 +104,9 @@ class ConnectionHandler:
             log.debug("[%s] 超时", self.conn_id)
         except ConnectionError:
             log.debug("[%s] 连接错误", self.conn_id)
+        except (asyncio.CancelledError, GeneratorExit):
+            # 正常关闭，不记录错误
+            pass
         except Exception as e:
             log.exception("[%s] 异常: %s", self.conn_id, e)
         finally:
@@ -329,6 +332,7 @@ class ConnectionHandler:
     async def _tunnel(self, dst_reader, dst_writer):
         """双向隧道转发。"""
         f1 = f2 = None
+        cancelled = False
         try:
             # 获取限速参数
             user = None
@@ -349,7 +353,9 @@ class ConnectionHandler:
             await asyncio.gather(f1, f2, return_exceptions=True)
 
         except asyncio.CancelledError:
-            pass
+            cancelled = True
+        except GeneratorExit:
+            cancelled = True
         except Exception as e:
             log.exception("[%s] 隧道异常: %s", self.conn_id, e)
         finally:
@@ -359,11 +365,12 @@ class ConnectionHandler:
                     task.cancel()
                     try:
                         await task
-                    except asyncio.CancelledError:
+                    except (asyncio.CancelledError, GeneratorExit):
                         pass
             self._close_streams(dst_reader, dst_writer)
-            # 记录最终统计
-            await self._record_stats()
+            # 记录最终统计 - 协程被取消时不做异步操作（避免 GeneratorExit）
+            if not cancelled:
+                await self._record_stats()
 
     async def _forward(self, src, dst, direction, speed_limit_mbps, user):
         """单向转发，带限速。"""