p2p/simulation: Test snapshot correctness and minimal benchmark (#18287)

* p2p/simulation: WIP minimal snapshot test

* p2p/simulation: Add snapshot create, load and verify to snapshot test

* build: add test tag for tests

* p2p/simulations, build: Revert travis change, build test sym always

* p2p/simulations: Add comments, timeout check on additional events

* p2p/simulation: Add benchmark template for minimal peer protocol init

* p2p/simulations: Remove unused code

* p2p/simulation: Correct timer reset

* p2p/simulations: Put snapshot check events in buffer and call blocking

* p2p/simulations: TestSnapshot fail if Load function returns early

* p2p/simulations: TestSnapshot wait for all connections before returning

* p2p/simulation: Revert to before wait for snap load (5e75594)

* p2p/simulations: add "conns after load" subtest to TestSnapshot

and nudge