refactor(server): move addPlayer implementation to ServerGameState

- Relocated `addPlayer` method from template-based `GameState` to `ServerGameState`.
- Updated method signature and comments for better clarity.

src/game/GameState.cpp

@@ -167,6 +167,13 @@ namespace UNO::GAME {
 
     ServerGameState::ServerGameState() : serverGameStage_(ServerGameStage::PRE_GAME) {}
 
+    void ServerGameState::addPlayer(ServerPlayerState playerState)
+    {
+        long long currentPlayerIndex = this->currentPlayer_ - this->players_.begin();
+        this->players_.push_back(std::move(playerState));
+        this->currentPlayer_ = this->players_.begin() + currentPlayerIndex;
+    }
+
     void ServerGameState::init()
     {
         while (discardPile_.isEmpty() || discardPile_.getFront().getType() > CardType::NUM9) {

src/game/GameState.h

@@ -175,12 +175,6 @@ namespace UNO::GAME {
 
         [[nodiscard]] size_t getDrawCount() const;
 
-        /**
-         * 向对局中添加玩家
-         * @param playerState 要添加的玩家状态
-         */
-        void addPlayer(PlayerStateType playerState);
-
         /**
          * 清空玩家
          */
@@ -235,15 +229,6 @@ namespace UNO::GAME {
         return this->drawCount_;
     }
 
-
-    template<PlayerStateTypeConcept PlayerStateType>
-    void GameState<PlayerStateType>::addPlayer(PlayerStateType playerState)
-    {
-        int currentPlayerIndex = this->currentPlayer_ - this->players_.begin();
-        this->players_.push_back(std::move(playerState));
-        this->currentPlayer_ = this->players_.begin() + currentPlayerIndex;
-    }
-
     template<PlayerStateTypeConcept PlayerStateType>
     void GameState<PlayerStateType>::nextPlayer()
     {
@@ -398,6 +383,12 @@ namespace UNO::GAME {
          */
         void init();
 
+        /**
+         * 向对局中添加玩家
+         * @param playerState 要添加的玩家状态
+         */
+        void addPlayer(ServerPlayerState playerState);
+
         /**
          * 由于用户摸牌而改变状态
          */