8 hours, turrets, pick ups and phases.
Pick ups have a max lifetime. This timer does not tick down if the player is not shooting or if the pick up is currently held by a walker. Turrets displace walkers just fine now, for real, please be for real this time. Removed timed phases gated by a do once because this led to phases bleeding over into sequential lives. Rewrote a few sections of code to be more readable / take less space. Fixed an issue where walkers that turned a pick up into a turret would have issues registering themselves as in contact with the turret because of new collision layers. These same walkers are now more consistently assigned to their build towers as trackers after the build completes. Flying shooters are threatening instead of big harmless health piles. The functionality for new flier spawner enrage state is in but unbalanced.