refactor(bot): remove cancel_pending_tasks function and adjust shutdown behavior

bot.py

@@ -1,5 +1,3 @@
-import asyncio
-
 import nonebot
 
 # from nonebot.adapters.discord import Adapter as DiscordAdapter
@@ -18,28 +16,7 @@ driver.register_adapter(OneBotV11Adapter)
 
 from zhenxun.services.db_context import disconnect
 
-
-async def cancel_pending_tasks():
-    """在关闭前尽量取消仍在运行的协程，避免关闭后继续访问数据库连接池。"""
-    loop = asyncio.get_running_loop()
-    current = asyncio.current_task(loop=loop)
-    pending = [
-        task
-        for task in asyncio.all_tasks(loop)
-        if task is not current and not task.done()
-    ]
-    if not pending:
-        return
-
-    for task in pending:
-        task.cancel()
-
-    await asyncio.gather(*pending, return_exceptions=True)
-
-
 # driver.on_startup(init)
-# 先取消可能在跑的任务，再断开数据库，避免 pool closing 异常
-driver.on_shutdown(cancel_pending_tasks)
 driver.on_shutdown(disconnect)
 
 # nonebot.load_builtin_plugins("echo")