feat: Implement `Quiz` model, service and repository

[apomalyn]

As a developer, I want a clear definition of a quiz, and a way to interact with the custom and premade quizzes.

Requirements

You can find the Quiz, and BaseQuiz definitions here

Update the User definition

Implement a service that:

• retrieve the list of quizzes from the local database
• sync the list with the API

Implement a repository that:

• retrieve the list of quizzes from the service
• keep it in memory

What needs to be done

• Update the User model: add savedQuizzes
• Using Freezed and Isar, implement QuizContent, QuizBase and Quiz model
• Create the QuestionFormat enum with the following value:
  • one_word
• Implement a service QuizService under src/practice/services. It should have the following methods:
  • List<Quiz> getAll(): retrieve all the quizzes in the local database
  • Future<void> synchronize(): call the API and synchronize the local list with the API (depends on https://github.com/RoadTripMoustache/kana_to_kanji_api/issues/32)
• Implement a repository QuizRepository as a listenable service under src/practice/repositories. Register it on the locator. It should have the following methods:
  • getter for List<Quiz> quizzes that load from the service all the quizzes if not already loaded
  • registered as listenToReactiveValues

Dependencies

Child of #160

Depends on:

• 135

• https://github.com/RoadTripMoustache/kana_to_kanji_api/issues/32
• https://github.com/RoadTripMoustache/kana_to_kanji_api/issues/67