Refactor VFL Client (DI for ClientTrainer)

[moreyhat]

Is your feature request related to a problem? Please describe.
No, it's just for refactoring the program.

Describe the solution you'd like
Introducing DI (Dependency Injection) for ClientTrainer.

Describe alternatives you've considered
N/A

Additional context
N/A

[moreyhat]

Closing this issue due to it is duplicated. See #8 .