[#11] feature: model and repository of creating game

[teds-lin]

實作以下部份並且新增相關測試案例：

• Domain models

  • Game -add_players()
    • 玩家人數限制為2~4人
    • bind Player instances to specific Game instance
  • id , identifier could be generated in UUID v4 format
  • assign_character(), 僅紀錄目前哪些調查員已被選擇，具體那個玩家選擇那個調查員由Player class紀錄

• Player

  • 紀錄選擇那個調查員

• In-memory repository

  • InMemoryRepository.save()
  • Using hash table to store key (game ID) value (relevant Game instance) pairs
  • Provide thread-safe access to the in-memory games dictionary