Implemented bonus for multiple players repairing #3748

This works by finding the square root of the amount of players repairing, and multiplying the base HP restored by that. The square roots are cached to prevent extraneous calculations. I also changed a  `for(;;)` to `while(true)` to aid code quality. It's all compiled into `GOTO`s anyways
`Repairers = Repairers.Where(player => player.WinState == WinState.Undefined || player.Stances[self.Owner] == Stance.Ally).ToList();` is preferred because it's more consistent with the rest of the codebase (need System.Linq for this too)