sorrys in PNNetwork.cycle_cover

[chi-p-3141]

Working on fixing the sorrys in PNNetwork.cycle_cover; got map_surj and map_deg to work (more elegantly than I expected, as Lean automatically closed the goals once simplified enough) but I can't currently figure out map_adj.
You can see my (partial) attempt commented out in the commit, working up until I try using hfinp to show that Port.to_FinPort preserves the port part of the pair.

(Unrelated: hope i correctly understood what "Draft pull requests' are for...)

[Shreyas4991]

Draft pull requests are for you to draft the PR and shape it. Normally this means, reviewers don't review the PR until you explicitly change this and mark the PR ready for review.

[Shreyas4991]

Please merge main (usually git pull origin main). This will change imports because PortNumbering and LOCAL have moved under the DGAlgorithms/Models/MessagePassing folder. The idea is to keep the "view-growing" models in a separate folder. Apologies for the merge-conflict.