Not even London lashing its October rains could keep the cream of the crop away from the British Film Institute’s Luminous Gala, a biennial event that sets out to raise funds for the preservation and advancement of the BFI National Archive. The archive is one of the world’s largest and most significant, preserving, housing, and promoting over a century’s worth of British film and television—from never-aired Charlie Chaplin outtakes to The Bridge on the River Kwai. It is as thorough a…