[Fix] Bugs where cleanup code is not executed correctly when bot exits

[ConnectionFailedd]

When bot exits, it sets _should_exit (1), so that Bot._handle_should_exit will be executed, which calls cancel_scope.cancel() (2):

class Bot:
    async def _run(self) -> None:
        """运行 AliceBot。"""
        logger.info("Running AliceBot...")

        for bot_run_hook_func in self._bot_run_hooks:
            await bot_run_hook_func(self)

        try:
            for _adapter in self.adapters:
                for adapter_startup_hook_func in self._adapter_startup_hooks:
                    await adapter_startup_hook_func(_adapter)
                try:
                    await _adapter.startup()
                except Exception:
                    logger.exception("Startup adapter failed", adapter=_adapter)

            async with anyio.create_task_group() as tg:
                for _adapter in self.adapters:
                    for adapter_run_hook_func in self._adapter_run_hooks:
                        await adapter_run_hook_func(_adapter)
                    tg.start_soon(_adapter.safe_run)

            await self._should_exit.wait()
        finally: # (3)
            for _adapter in self.adapters:
                for adapter_shutdown_hook_func in self._adapter_shutdown_hooks:
                    await adapter_shutdown_hook_func(_adapter)
                await _adapter.shutdown()

            for bot_exit_hook_func in self._bot_exit_hooks:
                await bot_exit_hook_func(self)

            self.adapters.clear()
            self.plugins_priority_dict.clear()
            self._module_path_finder.path.clear()

    def _handle_exit(self, *_args: Any) -> None:  # pragma: no cover
        """当机器人收到退出信号时，根据情况进行处理。"""
        logger.info("Stopping AliceBot...")
        if self._should_exit.is_set():
            logger.warning("Force Exit AliceBot...")
            sys.exit()
        else:
            self._should_exit.set() # (1)

    async def _handle_should_exit(self, cancel_scope: anyio.CancelScope) -> None:
        """当 should_exit 被设置时取消当前的 task group。"""
        await self._should_exit.wait()
        cancel_scope.cancel() # (2)

This makes the finally block in _run (3) not executed properly. According to my observation, the execution stops AFTER THE FIRST await.

Added with anyio.CancelScope(shield=True): line to fix this bug. It works on me.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (06afa44) to head (5c03934).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #176   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           12        12           
  Lines          932       933    +1     
=========================================
+ Hits           932       933    +1     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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[st1020]

LGTM, and we can add a test for this case.