feat(scala): m09 input/app/runtime and m10 extensions with tests

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scala/solutions/App.scala

@@ -0,0 +1,25 @@
+package snake
+
+/** m09 app: the whole game wired together as values: streams of actions in, a stream of drawings out. */
+object App:
+
+  val TICK_MS: Long = 150
+  val FRAME_MS: Long = 25
+
+  // Everything that can happen to the game: a Tick every TICK_MS, and an action for each bound key.
+  lazy val classicActions: Stream[Action] =
+    Stream.interval(TICK_MS).map(_ => Action.Tick).merge(Stream.keyDowns.filterMap(Input.keyToAction))
+
+  // m10: a Frame every FRAME_MS instead of a Tick; the game itself decides (movesEvery) which frames take a step.
+  lazy val speedActions: Stream[Action] =
+    Stream.interval(FRAME_MS).map(_ => Action.Frame).merge(Stream.keyDowns.filterMap(Input.keyToAction))
+
+  // Actions folded into game states. startWith puts the initial state first so it is drawn right away.
+  def states(seed: Long, actions: Stream[Action]): Stream[GameState] =
+    actions.scan(Spawn.newGame(seed))(Game.update).startWith(Spawn.newGame(seed))
+
+  def render(state: GameState): IO[Unit] = IO.drawScene(View.view(state))
+
+  // The whole program as a value: get a seed, then turn the stream of states into a stream of drawings.
+  // Nothing runs here; Runtime interprets it.
+  lazy val main: IO[Stream[IO[Unit]]] = IO.randomSeed.map(seed => states(seed, speedActions).map(render))