App hangs for a while when switching appearance

[gentlegiantJGC]

I assume there is a bit of work being done in the background to load and parse the files.
There should be some indicator to the user that it is working.

[jevexendo]

This is definitely something I've looked into implementing, however the setStyleSheet method doesn't seem to provide a way to monitor progress.

In reality, there's not much that I'm doing when it comes to updating the application theme, most of the work is being taken care of by Qt. The following code is just about all I need to run to trigger the update:

    def apply(self, application: QApplication) -> None:
        """Apply theme to a `QtWidgets.QApplication`."""
        application.setStyle(self._theme["style"])
        application.setStyleSheet(self._style_sheets["application.qss"])

I'd love to find a callback, signal, or really just anything that gives feedback on what Qt is doing after I hand this off, but I haven't found a way to get that information.