Friendships dissolve for a litany of reasons. Exasperation. Envy. Fallen scales from gradually or suddenly clearer eyes. Sometimes it’s a last straw; sometimes, an entire bale of hay, parked in plain sight, unnoticed for years. The reasons for the breakup in “The Banshees of Inisherin,” writer-director Martin McDonagh’s fourth feature, become clear in due course. But they’re not important, not really. Like “some fool of a moody schoolchild” or simply a man protective of his remaining time on his tiny, gorgeously forlorn (and fictional) island off the coast of Ireland, amateur pub fiddler and a…
