feat: prevent selection of suffix text in preferences spinboxes

[soleuniverse101]

(see issue #3802)

It was done by adding to the spinboxes an event filter that checks whether the selection or cursor are in a valid state.

I hope that I correctly followed the contribution guidelines regarding type hints. I had to cast some of the objects to pass the ninja mypy tests.

[dae]

Thank you for taking the time to contribute! I'm a bit nervous about unintended regressions here - it's a fairly unimportant issue, and any change can introduce unintended breakage. For example, we now get these errors when closing Anki:

Error in sys.excepthook:
TypeError: 'NoneType' object is not callable

Original exception was:
Traceback (most recent call last):
File "/Users/dae/Work/desktop/anki/qt/aqt/preferences.py", line 56, in eventFilter
assert isinstance(spinbox, QSpinBox)
AssertionError

[soleuniverse101]

Thank you for taking the time to contribute! I'm a bit nervous about unintended regressions here - it's a fairly unimportant issue, and any change can introduce unintended breakage. For example, we now get these errors when closing Anki:

Error in sys.excepthook: TypeError: 'NoneType' object is not callable

Original exception was: Traceback (most recent call last): File "/Users/dae/Work/desktop/anki/qt/aqt/preferences.py", line 56, in eventFilter assert isinstance(spinbox, QSpinBox) AssertionError

Sorry, I'm not completely familiar how Qt's types work and I think I misinterpreted how a certain function is called. I corrected the error you mentioned by properly testing the types of the objects I use in the event filter function. I wrongly assumed that I could cast them instead...

Thank you for pointing that out! I know that it's not a priority fix, I just wanted to start contributing to Anki with something small. I understand your concerns about introducing unnecessary change.