Decision rules on Sequencer forcing race-mode

[danlessa]

Related to #39

[jackhack00]

@danlessa
As we already have a treshold for gas cost (which, if current gas price is too high, prevents an actor from doing a transaction), we could do an easy hack for this decision rule:
If the payoff is too low, a Sequencer does not do a commitment bond or a reveal content tx (which forces racemode).
Payoff = Expected_Rewards - Costs (where we can use all current costs + a placeholder_cost )
Imo, this would be very simple, and would let us later add to the placeholder_cost - such as opportunity cost, private reasons for the Sequencer, a more specified decision rule that adds cost, etc.
Up to you though, if there is a better / simpler version to add this I'm fine with it!

[danlessa]

• compute payoff for forcing race mode on reveal content phase
• compute payoff for forcing race mode on commit bond phase
• force race mode if payoff < 0 on reveal content phase
• force race mode if payoff < 0 on commit bond phase

[danlessa]

Note: forcing race mode is equivalent to just waiting and do nothing cc @jackhack00

[danlessa]

Implemented by #85