Improve the "Learn ahead limit" and "Timebox time limit" dialogs

## The "Learn ahead limit" and "Timebox time limit" dialogs

- [x] Change them to input steppers (like in https://github.com/ankidroid/Anki-Android/issues/20477).
- [x] Prevent the user from typing more than 3 digits.
- [x] Replace "OK with "Save".
- [ ] Add a toggle to disable the limits like the screenshot bellow.
- [ ] Look into the leading zero issues discussed in https://github.com/ankidroid/Anki-Android/pull/20520#issuecomment-4095597664. I don't know if the fix there somehow fixes these dialogs too, but if it doesn't consider adding it to these.