In the Details By JENNIFER B. McDONALD   THE LIFESPAN OF A FACT By John D’Agata and Jim Fingal 123 pp. W. W. Norton & Company. Paper, $17.95. This book review would be so much easier to write were we to play by John D’Agata’s rules. So let’s try it. (1) This is not a book review; it’s an essay. (2) I’m not a critic; I’m an artist. (3) Nothing I say can be used against me by the subjects of this essay, nor may anyone hold me to account re facts, truth or any contract I have supposedly entered into with you, the reader. There are to be no…