KYIV (Reuters) – One of the fighters holed up in a steelworks besieged by Russian forces in the Ukrainian city of Mariupol has appealed to SpaceX billionaire Elon Musk to help evacuate them. Many civilians were rescued from the sprawling Azovstal plant last week under an agreement with Russia, but no deal has been reached with Moscow on allowing out hundreds of fighters, some of whom are wounded, after weeks of bombardment. “@elonmusk people say you come from another planet to teach people to believe in the impossible. Our planets are next to each other, as I live where it is nearly impossible…