tests(chat): add common `ChatHistorySerializerTests` and `LessonSerializerTests`
tests(chat): add common `ChatHistorySerializerTests` and `LessonSerializerTests`

raccoongang/socraticqs2,cjlee112/socraticqs2,cjlee112/socraticqs2,cjlee112/socraticqs2,raccoongang/socraticqs2,cjlee112/socraticqs2,raccoongang/socraticqs2,raccoongang/socraticqs2