test: add unit tests for Blackjack and TicTacToe

- Add xUnit test projects for both games
- Implement game flow tests for Blackjack
- Implement game flow tests for TicTacToe
- Rename namespaces and projects to follow `Game.*` convention
- Add documentation for testing games

Game.Blackjack/Singletons/GamePhase.cs

@@ -0,0 +1,10 @@
+namespace Game.Blackjack;
+
+public enum GamePhase : byte
+{
+    Betting = 0,
+    Dealing = 1,
+    PlayerTurn = 2,
+    DealerTurn = 3,
+    RoundOver = 4
+}

Game.Blackjack/Singletons/GameState.cs

@@ -0,0 +1,17 @@
+using MessagePack;
+
+namespace Game.Blackjack;
+
+/// <summary>
+/// Global game state stored on the singleton entity.
+/// </summary>
+[MessagePackObject]
+public struct GameState
+{
+    [Key(0)] public GamePhase Phase;
+    [Key(1)] public RoundResult Result;
+    [Key(2)] public int Chips;
+    [Key(3)] public int CurrentBet;
+    [Key(4)] public int RoundNumber;
+    [Key(5)] public uint Seed;
+}

Game.Blackjack/Singletons/RoundResult.cs

@@ -0,0 +1,12 @@
+namespace Game.Blackjack;
+
+public enum RoundResult : byte
+{
+    None = 0,
+    PlayerBust = 1,
+    DealerBust = 2,
+    PlayerWin = 3,
+    DealerWin = 4,
+    Push = 5,
+    Blackjack = 6
+}