feat(bot): 为 Bot 类的 __init__ 添加用于控制是否处理系统信号的 handle_signals 参数

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (7a58d41) to head (b5fb2d1). Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #140 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 11 11 Lines 874 875 +1 ========================================= + Hits 874 875 +1 ``` | [Flag](https://app.codecov.io/gh/AliceBotProject/alicebot/pull/140/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=AliceBotProject) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/AliceBotProject/alicebot/pull/140/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=AliceBotProject) | `100.00% <100.00%> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=AliceBotProject#carryforward-flags-in-the-pull-request-comment) to find out more.

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