💬 💡 rename some dataclass, add comments for events in mirai adapter

nonebot/adapters/mirai/event/meta.py

@@ -0,0 +1,31 @@
+from .base import Event
+
+
+class MetaEvent(Event):
+    """元事件基类"""
+    qq: int
+
+
+class BotOnlineEvent(MetaEvent):
+    """Bot登录成功"""
+    pass
+
+
+class BotOfflineEventActive(MetaEvent):
+    """Bot主动离线"""
+    pass
+
+
+class BotOfflineEventForce(MetaEvent):
+    """Bot被挤下线"""
+    pass
+
+
+class BotOfflineEventDropped(MetaEvent):
+    """Bot被服务器断开或因网络问题而掉线"""
+    pass
+
+
+class BotReloginEvent(MetaEvent):
+    """Bot主动重新登录"""
+    pass