Simulate clock skew

One idea for doing this would be to add a have a separate task queue per ProcessInfo, so that each process's clock evolves independently. Not sure what additional guarantees (if any) the clock for two processes on the same machine should provide.

Start by tracing the ProcessInfo clock and task-queue implementation mentioned in the issue. Define the guarantees that independently evolving process clocks should provide, then determine how clock-skew simulation can be tested across processes; the issue does not name specific files or tests.

Written by the indexing model from the issue text.