I removed the experiment flag for generics, removed the generics check (that hopefully won't be needed anymore), and removed all the native overrides that were added as work arounds for the lack of generics.

I added an override for async/atomic.Pointer[T any] to use a simpler design since we don't have to worry about atomics and to avoid some issues with casing the unsafe.Pointer. Without this override one of the tests fails around a nil *byte which may be caused by #843 (didn't look into to it too deeply since it made more sense to just override atomic.Pointer even if it did work).

This is related to #1013 and #1270