Run strong fuzz tests against NGC

[iphydf]

After #2291 is merged, we should add some setup code in protodump.cc to create/join a group and send+receive some messages. The protocol dump from that should then be used to run a longer term (several days) fuzz test against NGC.

[Green-Sky]

This was done manually TokTok/toktok-fuzzer#19

(@iphydf can we consider this done?)

[iphydf]

That PR is only toxsave, not the protocol. But: I've done it manually for several months on my machine, and nothing came up, so we can consider it done although I should make a PR for the code and run it on CI and on cron.