This changes the obstructionManager Spatial data to store pointers to the map data, instead of indices. This allows faster TestLine calls (and a few other cases).
Furthermore, with some care, this allows changing the structures from std::map to std::unordered_map, speeding up a few things further.

TODO: figure out how to do serialization / deserialization, because we need the same ordering and obviously pointers won't work.

It's not impossible that there is a third way to do this that's better, with e.g. an Entity-Map like thing.

An AI 2v2 reports this as a ~2% performance improvement.

^