refactor: separate action system responsibilities

tests/flat_map_baseline_test.gd

@@ -61,8 +61,9 @@ func _run() -> void:
 	)
 	worker.set_task(SimulationIds.ACTION_STUDY, 2.0)
 	worker.start_working()
-	worker.simulate_tick(village)
-	worker.simulate_tick(village)
+	var executor := ActionExecutionSystem.new()
+	executor.advance_npc(worker, village)
+	executor.advance_npc(worker, village)
 	_check(worker.task_complete, "A two-tick working task should complete")
 
 	var starving := SimNPC.new(
@@ -74,7 +75,7 @@ func _run() -> void:
 	)
 	starving.hunger = 100.0
 	starving.starvation_death_threshold = 1
-	starving.simulate_tick(village)
+	executor.advance_npc(starving, village)
 	_check(starving.is_dead, "Starvation threshold should still kill an NPC")
 
 	if failures.is_empty():