Convert from PySimpleGUI to PyQt6

[tbowers7]

PySimpleGUI moved to a subscription model on 1 July 2024, but this package (temporarily) points to an archived FOSS version of the GUI library until the various user interfaces can be ported to PyQt6.

[tbowers7]

This is partially dealt with in #50 .

The only other uses of PSG in this package remaining are deveny_grangle and deveny_collfocus, which will be consolidated in a new DeVeny GUI (#34).