Implement refueling logic for vehicles and update scene

Added refueling behavior for both air and ground vehicles, including approach, landing, and refueling stages for air vehicles and navigation to energy towers for ground vehicles. Updated Vehicle base class to support finding the nearest energy tower and tracking refueling state. Adjusted OrnithopterA fuel consumption, TankCombat NavMeshAgent height, and replaced/added prefabs in GameScene to reflect new refueling infrastructure.

Author: EnesEfeTokta