Effects regression in `copyto!(::Memory{Int}, ::Memory{Int}, ::Int)`

[LilithHafner]

In 1.11, Base.infer_effects(copyto!, (Memory{Int}, Memory{Int})) reports :noub. In 1.12-beta4 it does not. Relatedly, in 1.11 Base.infer_effects(Base.memmove, (Ptr{Base.Cvoid}, Ptr{Base.Cvoid}, Int)) reports :noub and in 1.12 it does not. In the memmove case, this :noub is suspect, but it would be nice to keep the :noub for copyto!.

[nsajko]

I guess you want this for the same reason as I do, for foldability? One issue is that adding noub would not help on its own, I think, because other effects, such as consistent, effect_free and nortcall would still be missing. I suppose implementing a pure-julia copyto!, without relying on ccall, might be the best solution, although it might hurt benchmarks a bit. I've been looking into exactly that for the past few days.