Improve timestamp updates

[gtrepta]

fixes: https://github.com/runtimeverification/firefly/issues/822

This PR introduces a <lastMineTime> cell, which helps to track the passage of time from the last mining of a block. This is necessary because <timestamp> can be manipulated in ways such as custom initialization, evm_revert and evm_increaseTime, which makes just updating the cell with #time() incorrect.

[ehildenb]

I'm somewhat skeptical of all the places we've added updates to the <lastMineTime> cell. Are we sure it's necessary in all of them, and not just when we're mining a block?

It may only actually be needed at the beginning of execution (by putting #time() in the initial configuration), and when we actually use the cell (the only place being where we say <lastMineTime> LASTTIME => #time() </lastMineTime>).

[ehildenb]

Let's add just an evm_increaseTime test which demonstrates the same failure we see on CI.