Last week, we discovered a but with `InvalidGossipCreator` accusations being thrown around incorrectly when many nodes were added to a parsec graph at once.
Given this kind of malice was newly detected, the presence of the bug wasn't too surprising; however, it should have been detected by the testing framework.
For this particular case, simply increasing the number of nodes in the `add_peers` tests allows to reliably catch the problem.
With this in mind, improve the integration tests for
- addition of multiple nodes
- removal of multiple nodes
- mix of additions and removals
Of course, all tests must respect PARSEC's invariant.