Refactor / rewrite the Week View's all-day events header widget code
We are talking about the "header" part of the view there (all-day events shown in the upper part), rather than the timetable (time-based events shown in the lower part), which works reasonably well. Refactoring the header code for reliability and maintainability would be fundamental blocker for the infinite timeline version of the weekview.
Quoting Georges' famous words in 2023-2024 regarding this code from 10 years earlier:
The week header code is the worst code I've ever written.
I dislike it with all my heart and soul.
It should be burned.
It is the source of many View: Week bugs, and particularly those linked below as related issues. Particularly, some heisenbug crashes like #757 and #1050. Quoting from #1050 :
The week header is the most delicate part of the codebase, so it's usually what crashes first, but every view might be victim of this misbehaviour.