Provided UseCases at ViewModelScope instead of Singleton

[Devendra34]

Fixes #116

Earlier all the UseCases were provided as singleton to each and every ViewModel. Means a single instance of a particular UseCase was shared across various ViewModels. In this way, even if any UseCases is not required by a ViewModel, it was still there in application level scope.
Now, all the UseCases are scoped by @ViewModelScope. Means it will be provided to a ViewModel only when it is required. Also If two (or more) ViewModels are using same type of UseCases then the instance of use-case for each of them would be different. (Read more in the articles mentioned below, especially the last two).
Articles referred:

1. Dependency Injection with Hilt
2. Using Hilt’s ViewModelComponent
3. Hilt View Models from dagger.dev

[hieuwu]

LGTM ! Nice. I love technical PRs including document and detailed explaination

[Devendra34]

LGTM ! Nice. I love technical PRs including document and detailed explaination

Thanks @hieuwu. I'm glad you liked the PR.
Kudos to you as well for maintaining such an awesome repository with best practices!