Getting polyscope parent window size/dimensions for callback

Start by comparing the C++ source's parent-window sizing and docking updates with the Python callback path using the imgui bindings. Determine whether the reported window and content-region values expose the needed parent context, then define the scope for sizing access, callback renaming, and control of the Structure, Picker, and Polyscope elements.

I'm creating custom UI elements since the default callback seems to only support a single additional window and also has a hardcoded name of "Command UI". In the C++ source, I noticed the windows are being docked by continually updating the current window heights of the parent window and adjusting the positions accordingly.

I'm trying to do this in the Python implementation with the imgui bindings, but the functions GetWindowHeight() and GetWindowWidth() seem to return completely static values when I call them within my callback, and do not change if I move/resize the parent window or the actual callback GUI element. It's unclear what it's doing. I'm seeing the same trouble with GetWindowContentRegionMax() and GetContentRegionMax().

Not sure if this is a ImGui specific question but it seems related to PolyScope. For that matter, it would be nice if the main polyscope instance could return the window sizing params for this purpose if the above bindings don't actually have the parent window context. Otherwise, I'm not sure how to get GUI elements to dock to different sides of the window, etc. It would also be nice if we could rename the default callback GUI, as well as enable/disable the Structure, Picker, and Polyscope GUI elements from Python like that can be done in C++. Additionally, further customization of those default elements would be highly appreciated since without it, users who want to customize the UI will have to turn off the boilerplate and re-write it which defeats the purpose in my opinion.