Reduce the number of path finds per frame.

[andriyDev]

Currently, agents will repeatedly look for a path until one is found, every frame. This can be very bad if lots of agents can't find a path to their respective targets.

Some easy things to try are:

1. Limit the number of nodes that are explored - give up after some limit.
2. Add a "priority accumulator" - only find paths for the top N agents, and when an agent fails to find a path, have their priority be significantly reduced.
3. Compute regions for the nav mesh and skip paths for nodes in different regions.