random-wta: Save random state to file instead of stderr

Hides ugly debug output from stderr but instead persists it in the generated
file, in case someone wants to re-generate it (e.g. after fixing a bug in the
generator).

src/random-wta/Main.hs

@@ -111,6 +111,7 @@ main = do
     Just x  -> setStdGen x
 
   withSpec opts $ \spec -> do
-    getStdGen >>= hPutStrLn stderr . ("Random state: " <>) . show
+    randGen <- getStdGen
     wta <- runGenerator (GeneratorConfig spec (optZeroFrequency opts)) genWTA
+    putStrLn $ "# Random state for this automaton: '" <> show randGen <> "'"
     T.putStr (Build.toLazyText (buildWTA wta))