use `dir()` and `getattr()` instead of `__dict__` in order to be
compatible with whatever magic modules decide to do to in the future.

Although PyQt6 doesn't currently do such magic, PySide6 does (discovered
when running similar code to check if there are any aliases PySide6
doesn't define), it does some lazy-loading of the module `__dict__`, so
to be a but more future-proof, access module and class attributes in
the official way.