By Satoshi Sugiyama and Chang-Ran Kim NARA, Japan (Reuters) -Former Prime Minister Shinzo Abe, the longest-serving leader of modern Japan, was gunned down on Friday while campaigning for a parliamentary election, shocking a country where guns are tightly controlled and political violence almost unthinkable. Abe, 67, was pronounced dead around five and a half hours after the shooting in the city of Nara. Police arrested a 41-year-old man and said the weapon was a homemade gun. “I am simply speechless over the news of Abe’s death,” Prime Minister Fumio Kishida, Abe’s protege, told reporters. Ear…