Type-instability because of @threads boxing variables

Hm, I’m wondering why. Do you have any suspicion?

In a recent thread I had a pretty big kernel, which was speed up by Polyester.

I’m not sure if profiling information is always 100% exact (for example I don’t even know if and how macros have to manage LineNumberNodes) and believe to have seen some oddities when profiling. Never bothered enough to investigate (especially as I prefer an outdated profiler).