Why aren't we building the extensions in parallel?

Per most recent Slicer hangout meeting notes, the next stable 5.12 will still require Rosetta for Apple Silicon Macs. There are likely additional build dependencies and build updates to make native arm builds possible. An Apple Silicon Mac will also need to be identified that will do the Slicer factory building, packaging and testing. Of course part of this work is making sure various parts extensions (primarily the compiled ones) are also still working on arm architecture. There are arm systems running Windows, Linux and macOS so it could be for all platforms.