Expose path iterator on Router<T> (similar to PathTrie<T>). Possibly `toDot` as well.

[nielsenko]

PathTrie<T> supports iterating over the registered paths, and even forming a graph of the DFA via toDot. We should expose the same for Router<T> for easier debugging of miss-routes

This came up in a discussion with @vfiruz97 on slack.