riverpod migration

[Shreemanarjun]

I have tried to complete riverpod migration in this repo. Its completed.
Will create PR with previous file structure soon.

(https://github.com/Shreemanarjun/flutter_puzzle_hack_riverpod)

[Roaa94]

Hi there, thanks a lot for your efforts and contribution in the previous PRs 🙏🏼
I appreciate your effort to migrate to Riverpod, however I'm doing a major restructure and cleanup of the code (#10) and adding testing while doing the migration, I also would like to not use ChangeNotifierProvider.

[Shreemanarjun]

Thanks . I think state notifier or New Notifier class will be the perfect replacement of change notifier .