Replace nnpy with pynng.

[fruffy]

nnpy has been deprecated four years ago and shows signs of bit-rotting. Installing it on newer distributions seems to cause issues. This is a draft to replace nnpy with pynng.

The reason nanomsg is very useful is because it allows us to model network switch behavior without requiring veths. And without veths we do not need sudo. When working with agents, a tight feedback loop can be useful, which includes running packet tests. sudo requirements can get in the way of that.

Related PRs: p4lang/behavioral-model#1361 p4lang/p4c#5576

[jafingerhut]

Is there some dependency or order that the several nnpy -> pynng PRs on different repos should be merged?

[fruffy]

Is there some dependency or order that the several nnpy -> pynng PRs on different repos should be merged?

I think PTF -> BMv2 -> P4C is the order. I need to check how much third-party still plays a rule. It might make sense to also get rid of depending on it in behavioral-model. Just use it to build the docker image, like we do in P4C.

This way we can make coordinates changes like this much simpler.

[jafingerhut]

Looks reasonable to me. I am at least half-way going with the passing of CI tests here, but I did skim through the changes and they look reasonable, given that I have little knowledge of the details of either nnpy or pynng. I would like to go through ptf -> bmv2 -> p4c updates for this and ensure they all play well together, but seems low risk.

[jafingerhut]

@fruffy If you have permission to merge the ptf, bmv2, and p4c pynng PRs, please go ahead. Or if you prefer I can do it.