fast_forward misleading name

[austinabell]

Intuitively I would expect fast_forward to progress the state transitions as if the time had passed naturally. Opening issue because I (and potentially others) might be surprised to find out it just progresses the block height, timestamp, and epoch and leaves the current in-flight transactions as-is.

My argument for why it should progress the transactions is that testing transaction ordering is very non-deterministic and relies on manually waiting in tests. Having fast_forward progress the transactions doesn't solve the non-determinism, but can make it much harder to hit.

At very least, the docs for fast_forward should indicate that any receipts that are scheduled and have not been executed will not be progressed during this call, I think.