Pathfinding is way too slow

**Describe the bug**
Pathfinding bogs down when you start building moderate numbers of ships and/or exploring moderate numbers of star systems. (Not sure what's triggering it.)

**To Reproduce**
Steps to reproduce the behavior:
1. Play the game for a while.
2. Process a turn

**Expected behavior**
Turn should process in a reasonable amount of time.

**Actual behavior**
Turn takes forever due to pathfinding.

**Screenshots**
N/A

**Additional context**
This seems to be caused by finding warp point exits which is calling ability lookup functions over and over again... We can't cache abilities here, can we?