You can read it online, or — better — you can sweat it out in its completed form when it opens in wide release this week. Either way, the screenplay for the German thriller “The Teachers’ Lounge” is so tight it squeaks, each new development in a series of unfortunate events clicking into place like a turn of a Rubik’s Cube — which provides the film with a visual leitmotif. Not since “The Bear” has there been anything so universally described as nerve-wracking, in such admiring ways. And by minute 3, the tension’s building as if we were already reaching a dramatic climax. Set in a secondary sch…