GetState / SetState are not a good idea in the Year of our Lord 2025

[emersonrp]

Back when I had no idea what I was doing, putting access to the various controls behind Page's GetState / SetState seemed like a useful abstraction, but in reality, since GetState can return str|bool|list|dict|Colour|etc, it makes type-checking a complete headache.

Undoing this historical decision would be tangly but would lead to better code in the long run.

Labeling this as "enhancement" but it's arguably "bug".

Edit to add: this one can be fixed piecemeal, removing chunks of GetState() in places a bit at a time. Each improvement will help.

[emersonrp]

Additional thought, though this might want to be a separate issue, lumping all of the named controls into one self.Ctrls[] dict is a related and even worse type-checking hassle. Not clear what the path forward is on that, since we need to iterate Pages' controls lists in many places.