use once_cell's unsync variant instead of the sync variant
We generally use once_cell::sync::OnceCell
and once_cell::sync::Lazy
instead of once_cell::unsync::OnceCell
and once_cell::unsync::Lazy
we should replace it since we don't need our objects and widgets to be Sync
and most of them already aren't Sync
anyway.
Edited by Julian Sparber