Currently, we don't close MemorySegments that we pass to upcalls. This makes it easier to leak a MemorySegment from an upcall, but it also incurs an additional copy on Windows and Aarch64, and forces users to close these segments manually instead.

We can instead registers these segments with a NativeScope that is closed after the upcall completes, to make sure these segments do not leak inadvertently, and we don't need the additional copy on some platforms.