Add utility methods to `ctx` by sublcassing it

[Paillat-dev]

Add utility methods to ctx, for example ctx.error that allow to show an error (ex. a parameter is required when used in combination with another) while staying in theme with the other errors. Maybe it could even then be used inside of the error_handler ext. to send the errors.

For reference:

• https://github.com/Pycord-Development/pycord/blob/master/examples/custom_context.py

[ItsDrike]

Slightly afraid what pyright will think here, it might cause issues, but if it'll work fine, it could be worth doing.