Pretty much from its first moment to last, Ahmir “Questlove” Thompson’s “Summer of Soul,” a film chronicling six magical Sundays of stirring soul music holding forth as the “Harlem Cultural Festival” at Mount Morris (now Marcus Garvey) Park in 1969, shows why it’s been a summer-long rage since its July debut streaming on Hulu and in theaters nationwide. Thompson distilled some 40 hours of meticulously crafted footage shot by a four-camera crew led by the late Hal Tulchin into a 117-minute documentary that includes a laundry list of the greatest soul and gospel acts of the era It all kicks off with 19-year-old…