Migrate PrefController to Riverpod Provider

[davidetarsi]

This pull request refactors the PrefController class by replacing it with a Riverpod provider generated using the Riverpod code generator in Flutter.

Changes made:

• Removed the PrefController class, which previously handled preference state management.
• Created a new Riverpod provider to manage preferences, leveraging the Riverpod code generator for cleaner and more maintainable code.
• Refactored dependent widgets to consume state using ref.watch() and ConsumerWidget.

Benefits:

• Improved state management following Riverpod's best practices.
• Enhanced scalability and maintainability of the codebase.
• Cleaner and more testable architecture through dependency injection.