Added custom date setter and dev feature flag

[gonfff]

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[Copilot]

Pull request overview

This PR adds a testing date override feature that allows developers to set a custom system date for testing purposes, controlled by a compile-time feature flag (ENABLE_TESTING_DATE).

Changes:

• Introduces AppClock class as a centralized abstraction for date/time operations with override capability
• Adds UI in settings screen to select and manage the testing date override
• Integrates the clock abstraction throughout the app, replacing direct DateTime.now() calls with nowProvider() in key areas

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
lib/application/app_clock.dart	New clock abstraction with date override support and feature flag
lib/domain/repositories/settings_repository.dart	Added methods for persisting testing date override
lib/infrastructure/repositories/drift_settings_repository.dart	Implementation for storing/retrieving date override from storage
lib/application/settings/get_testing_date_override_use_case.dart	Use case for retrieving stored testing date
lib/application/settings/set_testing_date_override_use_case.dart	Use case for persisting testing date
lib/application/app_dependencies.dart	Integrated AppClock and testing date use cases into dependency injection
lib/main.dart	App initialization to load and apply testing date override
lib/presentation/types/settings_callbacks.dart	Added callback type for testing date changes
lib/presentation/screens/settings_screen.dart	UI for selecting and resetting testing date override
lib/presentation/widgets/settings_sheet.dart	Passes testing date parameters to settings screen
lib/presentation/screens/subscriptions_screen.dart	Integrates clock provider and refreshes on date changes
lib/presentation/screens/analytics_screen.dart	Uses clock provider for date calculations
lib/presentation/widgets/add_subscription_sheet.dart	Uses clock provider for default dates
lib/presentation/screens/currency_rates_screen.dart	Uses clock provider for date boundaries
lib/presentation/viewmodels/subscriptions_view_model.dart	Uses clock provider and adds refresh method for date changes
lib/presentation/l10n/app_localizations.dart	Adds localization strings for testing feature in English and Russian
test/application/app_clock_test.dart	Tests for AppClock override functionality
test/application/settings/testing_date_override_use_cases_test.dart	Tests for date override use cases
test/presentation/l10n/app_localizations_test.dart	Updated to verify new localization keys

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