AT THE MOVIES, David Cronenberg’s cult horror flick Scanners invades the minds of moviegoers. IN MUSIC, five weeks after his death, John Lennon tops the Billboard charts with the single “(Just Like) Starting Over” and the LP Double Fantasy (right). IN BOOKSTORES, scores of readers take a trip through Carl Sagan’s Cosmos, which is No. 1 in the New York Times’ non-fiction universe. AND IN THE NEWS, the Iranian hostage crisis heats up as President-elect Reagan prepares for his inauguration. The captives were freed five days later, the same day as Reagan’s swearing in.