PORT SUDAN, Sudan — Famine. Massacres. And now badly needed food and other supplies are under strain. Sudan on Wednesday entered a fourth year of a war that’s been called an “abandoned crisis,” as a new Middle East conflict throws into shadow the fighting that has forced 13 million people to flee their homes. The North African country is described as the world’s largest humanitarian challenge, notably in terms of displacement and hunger. There is no end in sight to the fighting between the