SpinButton entry

[sonnyp]

https://docs.gtk.org/gtk4/class.SpinButton.html

A good example would be 2 spinners to select hours and minutes.

See https://gitlab.gnome.org/verdre/Capsule/-/blob/main/src/AddTherapyDialog.ui#L182 in https://flathub.org/apps/nl.v0yd.Capsule

[sonnyp]

Ok so there is a WIP PR, but the author hasn't replied. We can take over and finish it for them. #248

Feel free to make a new PR and use their work or start from scratch.