feat: enforce activity site capacity

simulation/SimulationManager.gd

@@ -395,6 +395,18 @@ func synchronize_npc_position(npc_id: int, active_position: Vector3) -> bool:
 	return false
 
 
+func get_activity_target_claim_count(target_id: StringName, except_npc_id: int = -1) -> int:
+	var count := 0
+	for npc in npcs:
+		if npc.id == except_npc_id or npc.is_dead:
+			continue
+		if npc.target_id != target_id:
+			continue
+		if npc.task_state in [SimNPC.TASK_STATE_TRAVELING, SimNPC.TASK_STATE_WORKING]:
+			count += 1
+	return count
+
+
 func _npc_inventory_id(npc_id: int) -> StringName:
 	return StringName("npc_%d_inventory" % npc_id)