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
A linebreak after the `|| ` would be nice to prevent long single lines of code.