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.