Clarify errors when a user is using a Scope requiring action outside of a Scope

[markehammons]

As a user, it can be confusing to see an error like "Allocator not found" when using operations like Ptr.copy. Especially because it's not quite clear how to get an Allocator for such operations.

This ticket is complete when a solution has been found that directs the user on how to properly use functions that require allocators.