Rewrite main.py

[TheWever]

Rewrite main.py to refactor and clean up the existing code, improving both readability and usability.

Currently, bot-related events, user settings, and other functionalities are all mixed together in main.py, which should solely be responsible for running the bot.
This structure makes it difficult to change configurations and reduces readability.
The code itself should also be refactored.

• Move the user settings to a new configuration file (config.*)
  • I suggest using a config.toml file along with a config.py module to parse the configuration.
• Remove bot-specific code from main.py as much as possible
  • Consider creating a bot subclass (e.g., bot.py) or using cogs
• Clean up existing code