Implement game summary calculation

src/main/kotlin/rps/Game.kt

@@ -34,4 +34,9 @@ fun determineOutcome(first: Move, second: Move): Outcome = when {
   else -> Outcome.LOSS
 }
 
-fun calculateGameSummary(turns: List<Outcome>): GameSummary = TODO()
+// Note: This would be slightly more efficient (but a lot less elegant) with an imperative loop and three mutable integers.
+fun calculateGameSummary(turns: List<Outcome>) = GameSummary(
+    wins = turns.count { it == Outcome.WIN },
+    draws = turns.count { it == Outcome.DRAW },
+    losses = turns.count { it == Outcome.LOSS },
+)