Amnesty International has issued an ''urgent action'' notice, calling on human rights activists around the world to send appeals asking Fidel Castro and other Cuban government officials to provide immediate medical attention to and the unconditional release of an imprisoned opponent on a prolonged a hunger strike. Leonardo Miguel Bruzón Avila has been in jail for more than a year and has not yet been charged or given a trial, Amnesty International said. His deteriorating health has raised concern on and off the island. ''We send out urgent action notices when we fear that somebody's life is in danger,'' said...