fix: SOCKS5 隧道连接超时

修复子线程事件循环中 asyncio.wait_for 包装 open_connection 导致的读取取消问题。
改用 socket 层面的 timeout 设置，不再用 wait_for 包装。

同时修复 _reply 中 writer.write 不需要 await 的问题。

engine/server.py

@@ -4,6 +4,7 @@ import logging
 import struct
 import time
 import uuid
+import socket as _socket
 import ipaddress
 from datetime import datetime, timezone
 
@@ -127,11 +128,11 @@ class ConnectionHandler:
         methods = header[2:2 + n_methods]
         # 检查是否支持
         if METHOD_USERPASS in methods and self.config.auth_method == "userpass":
-            await self.writer.write(bytes([SOCKS_VERSION, METHOD_USERPASS]))
+            self.writer.write(bytes([SOCKS_VERSION, METHOD_USERPASS]))
         elif METHOD_NO_AUTH in methods:
-            await self.writer.write(bytes([SOCKS_VERSION, METHOD_NO_AUTH]))
+            self.writer.write(bytes([SOCKS_VERSION, METHOD_NO_AUTH]))
         else:
-            await self.writer.write(bytes([SOCKS_VERSION, METHOD_NOT_ACCEPTED]))
+            self.writer.write(bytes([SOCKS_VERSION, METHOD_NOT_ACCEPTED]))
             return False
         await self.writer.drain()
         return True
@@ -177,14 +178,14 @@ class ConnectionHandler:
             log.warning("认证失败: %s (user=%s)", self.src_ip, username)
             await self.user_service.log_event("auth_fail", username,
                                                self.src_ip, "密码错误或账号不可用")
-            await self.writer.write(bytes([1, 0x01]))  # auth fail
+            self.writer.write(bytes([1, 0x01]))  # auth fail
             await self.writer.drain()
             return False
 
         self.username = username
         log.info("[%s] 认证成功: %s (from %s)", self.conn_id, username, self.src_ip)
         await self.user_service.log_event("auth_success", username, self.src_ip)
-        await self.writer.write(bytes([1, 0x00]))  # auth ok
+        self.writer.write(bytes([1, 0x00]))  # auth ok
         await self.writer.drain()
         return True
 
@@ -273,11 +274,13 @@ class ConnectionHandler:
 
         # 连接目标
         try:
-            reader, writer = await asyncio.wait_for(
-                asyncio.open_connection(addr, port),
-                timeout=self.config.timeout
-            )
-        except (asyncio.TimeoutError, OSError) as e:
+            # 注意：不用 asyncio.wait_for 包装 open_connection，
+            # 在子线程事件循环中 wait_for 会导致连接成功后读取被取消
+            sock = _socket.socket(_socket.AF_INET, _socket.SOCK_STREAM)
+            sock.settimeout(self.config.timeout)
+            sock.connect((addr, port))
+            reader, writer = await asyncio.open_connection(sock=sock)
+        except (OSError, Exception) as e:
             log.warning("[%s] 无法连接 %s:%d: %s", self.conn_id, addr, port, e)
             rep = REP_CONN_REFUSED if "refused" in str(e).lower() else REP_HOST_UNREACHABLE
             await self._reply(rep)