A PROJECT AUDION EXTRA: The Adventures of Stan Slade, "The Burmese Penguin Caper"   What do you do if you grew up listening the classic dramatic series on the radio, then found a career writing TV comedy for Bob Hope, and now, decades later, you still harbor fond feelings about those radio shows of your youth? Well, if you're Robert L. Mills, you write shows like the one you're about to hear.  It's a takeoff of a certain famous detective whose name sounds awfully similar to OUR show's hero, named Stan Slade. The original "Adventures of Sam Spade" was broadcast in the late 1940s and early '50s. It starred Howard Duff as the detective created by Dashiell Hammett. It was a fun show that never took itself entirely seriously. Mr. Mills has nudged his tribute a little further into the tongue-in-cheek -- or should I say tongue in beak? -territory, reuniting the detective with his old adversaries from the Maltese Falcon movie, Sydney Greenstreet and Peter Lorre. Everyone in our cast gets to have some fun with this adventure of Stan Slade, Detective, entitled "The Burmese Penguin Caper".