A better robot charging heuristic

[typecasto]

What?

Robots should only charge at roboports that are closer to the destination than their last charging station was, instead of closer than they are.

Why?

In 2.0, robots will now only charge at roboports closer to their destination than the robots themselves are, to avoid a loop where they constantly charge at the same roboport(s) without ever making any progress, but this can create unintended scenarios where robots will ignore a perfectly good charging station just because their battery happened to run out after they already passed in front of it. In practice, this leads to a lot of robots running out of energy and traveling at slow speed for seemingly no reason, locked out of a perfectly good charge station just because of how the distances happened to work out. This new heuristic would essentially give robots one charge worth of leeway to ensure it is still making progress without causing unnecessary slowdowns.