Generic Typesafe LinkedList

[ityonemo]

After browsing some of the commentary here:
https://news.ycombinator.com/item?id=43679707

It seemed like a lot of people were concerned about the safety of the new linked list implementation. This PR includes SinglyLinkedList.Simple which is a generic wrapper over the SinglyLinkedLinkedList implementation details that enforces type safety and also provides a, possibly more intuitive type signature wherein the payloads themselves are added into the list.

If this is rejected, I don't mind, I think I only spent about 30 minutes on it.

#23590

[ityonemo]

as a slight bikeshedding aside, when I was writing this code, I found it the name of the 'Node' datatype to be confusing, and would have rather 'Node' be the name of what is called 'Payload' in the 'Simple' implementation, with 'Node' being renamed to 'NodeInfo' or possibly 'Links'. However, this was not included in this PR.