By Natalia Zinets KYIV (Reuters) – Ukraine hailed the defenders of the strategic city of Mariupol on Tuesday as heroes who changed the course of the war with Russia by keeping Russian forces at bay for 82 days of siege and bombardment. More than 250 fighters, some of them seriously wounded, have been evacuated after spending weeks in bunkers and tunnels below the sprawling Azovstal steel works in Mariupol where they had little food, water, medicine or other supplies. Their defiance meant Russia could not free up troops to fight on other fronts, a factor which Kyiv said had helped Ukrainian for…