use real method for `warn` and `fatal` to improve UX

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warn method and fatal method of BoundLogger are created with warn = warning, make both pycharm and vscode not automatically add ( after auto-complete, write a real method like def warn(self, event: str | None = None, *args: Any, **kw: Any) -> Any: will help this.

This is not a big issue but it would be nice to improve UX.