Volatile DB: port q-s-m tests to new infrastructure

Port the existing q-s-m tests to use the high-level interface described in https://github.com/advancedtelematic/quickcheck-state-machine/pull/355. As the VolatileDB has no references (no iterators or readers), `Test.StateMachine.Lockstep.Simple` can be used instead of `Test.StateMachine.Lockstep.NAry`.

@edsko warned me that this interface will likely need some changes before we can adopt it. It might be a good idea to make a local copy of that q-s-m infrastructure so that we can quickly modify it instead of having to submit PRs against the upstream repo and wait for them to get merged.

Best to wait until https://github.com/input-output-hk/ouroboros-network/pull/2534 is merged.