Optimize some collections

[ike709]

Pulls the low hanging fruit out of https://github.com/OpenDreamProject/OpenDream/pull/2023 since the other collections I touched in that PR need some more finagling than I initially realized.

The change to InheritingTypes is to reduce the number of allocated lists at the cost (aside from game setup) of doing a nullcheck in typesof().

Confirmed Paradise doesn't explode.