Bump requirement to pyside6.

[bvarner]

feat: Requirement bump to pyside6 cleanup: Removed requirement for qimage2ndarray. Conversion was only one-way, and ndarray is pretty straightforward to convert to QImage. Library did not have a release for pyside6.

In testing out loading UI files with QUILoader, I found some corner-case issues with pyside2 that were known. (I've lost the links... sigh)

So I've isolated my changes to move to pyside6, which reportedly does not suffer the same issues -- opening the door for not needing to pre-transpile the qt designer file into python.

[TheAntTeam]

Hi @bvarner, I think it's a nice idea that we would like to place it in a dedicated branch, to test it fully for different functionalities and OSes, and then merge it when we see that there are no problems.

To tell you the whole story, when we started developing the application QT6/pyside6 was just being released, and we considered it for some time, but we realized that it was still not fully ported and mature enough, and we decided to stick with QT5/pyside2, also if there was the inconvenient of the loader.

Maybe now it's a good time to switch to pyside6 and we greatly appreciate your contribution for this activity.

If you want we could make a branch called pyside6 and you could PR on it, or tell us if you think there is a better way.

[bvarner]

I think the better question is 'what kind of branching model do you intend to follow for this project'?

As a random guy making PRs I'm not sure I'm the person who should answer that.