(When) should `ManagedAtomic`/`UnsafeAtomic` be marked `Sendable`?

[lorentey (Karoy Lorentey)]

@glessard

The Unsafe versions are not as clear, because nothing in them controls the lifetime of the memory location they refer to. I’m not concerned about the semantics of using the type but about the requirement to manage the lifetime of the memory location.

I believe this is the same (or better) situation as with Unsafe(Mutable)(Buffer)Pointer, which are Sendable.