refactor: track background tasks in application lifecycle and clean up codebase

tests/test_shutdown_voice_cleanup.py

@@ -40,8 +40,9 @@ class ShutdownVoiceCleanupTests(unittest.IsolatedAsyncioTestCase):
         mock_guild.me.voice.channel = MagicMock()
         mock_guild.change_voice_state = AsyncMock()
 
-        with patch.object(type(self.bot), "voice_clients", [mock_vc]), patch.object(
-            type(self.bot), "guilds", [mock_guild]
+        with (
+            patch.object(type(self.bot), "voice_clients", [mock_vc]),
+            patch.object(type(self.bot), "guilds", [mock_guild]),
         ):
             await self.bot.disconnect_all_voice()