refactor: use riverpod for task progress bar

[matthiasn]

This pull request includes various changes aimed at improving the codebase by removing unused imports, refactoring existing classes, and introducing new state management for task progress. The most important changes include the removal of unused methods, the introduction of the TaskProgressState class, and the refactoring of the LinkedDuration widget to use Riverpod for state management.

Removal of Unused Methods and Imports:

• Removed the watchLinkedTotalDuration method from the JournalDb class in lib/database/database.dart.
• Removed unused imports in lib/database/database.dart and lib/features/journal/state/entry_controller.dart [1] [2].

Introduction of Task Progress State:

• Added the TaskProgressState class to manage task progress and estimate durations in lib/features/tasks/model/task_progress_state.dart.
• Generated code for TaskProgressState using Freezed in lib/features/tasks/model/task_progress_state.freezed.dart.

Refactoring for State Management:

• Refactored the LinkedDuration widget to use Riverpod for state management, replacing the previous StreamBuilder implementation in lib/features/tasks/ui/linked_duration.dart [1] [2] [3].
• Updated the TaskSliverAppBar to use the new LinkedDuration implementation in lib/features/tasks/ui/task_app_bar.dart.

Task Progress Controller:

• Introduced the TaskProgressController class to manage task progress state in lib/features/tasks/state/task_progress_controller.dart.
• Generated code for TaskProgressController using Riverpod in lib/features/tasks/state/task_progress_controller.g.dart.

Version Update:

• Updated the version of the project in pubspec.yaml.