Prepare tests for a bug where a block is missing when some witness sets a future time.

The test involves a network with 21 witnesses, out of which 4 have their time set to the current time plus 4 seconds. This causes these witnesses to produce their blocks too early, resulting in a "race" with witnesses who produce blocks according to the schedule. As a result, by other witnesses. In this scenario, the block from the correct witness is lost, and the witness receives a virtual operation called "producer_missed_operation".