refactor(peer) some _minor_ safety features

This PR cleans up the peer package, making it a tiny bit safer to use.

* All peers are created using Peerstore. It is no longer simple to instantiate a naked peer. To create naked peers, use the `mockpeer` package.

(This refactor was performed because of work #416 and a promise I made a long time ago)
I want to keep this as a Datastore. this abstraction doesnt hurt anything here. while it is not a TODO to make it persistent, we have the option to.