Rename module and add init file to conform to ruff.

.vscode/launch.json

@@ -8,7 +8,7 @@
         "name": "Python: Module",
         "type": "debugpy",
         "request": "launch",
-        "module": "off-cooldown-bot.main",
+        "module": "off_cooldown_bot.main",
         "justMyCode": true
     }
   ]

off_cooldown_bot/__init__.py

@@ -0,0 +1 @@
+"""Empty init file for off_cooldown_bot module."""