I don't think we need to put these methods into this module...they can just exist as direct singleton methods on the `MemoizedHelpers` module.  Singleton methods don't get added to the host class when the module is mixed in so there's no danger of "leaking" these methods into the user's namespace.

Plus, I think it's kinda confusing that the code below looks for a module named `LetDefinition` and this one is also called `LetDefinitions`, but the module it is looking for is not this module....it's `example_group::LetDefinitions`.