graphics/qview: Update to 7.1 and switch to qt6

Take maintainership.
Update pkg-descr.

https://github.com/jurplel/qView/releases/tag/7.0
https://github.com/jurplel/qView/releases/tag/7.1

PR: 289331
Approved by: danfe (maintainer timeout > 3 months)
Approved by: osa (mentor)