feat: add PlanningDurationService for estimating planning duration

- Implemented PlanningDurationService to provide an indicative wait time before calculation based on user input and calendar settings.
- Introduced duration estimation logic that considers horizon dates, balances, and rules without triggering a calculation.
- Enhanced user input component to display estimated duration using the new service.
- Updated translation files to include new duration estimate strings in multiple languages.
- Added tests for PlanningDurationService to ensure accurate duration estimation and calibration.
- Refactored leave planner service to remove hardcoded deadlines and improve worker responsiveness.

src/app/services/user-input-service.ts

@@ -107,6 +107,7 @@ export class UserInputService {
 	);
 	readonly remainingVacationDaysSignal = signal<VacDay[]>([]);
 	readonly computeTriggerSignal = signal(0);
+	readonly computationRequestedAtMs = signal<number | null>(null);
 
 	public updateBalances(updater: (balances: VacDay[]) => VacDay[]): void {
 		this.vacationNumberSignal.update(updater);
@@ -129,6 +130,7 @@ export class UserInputService {
 	}
 
 	public requestComputation(): void {
+		this.computationRequestedAtMs.set(performance.now());
 		this.computeTriggerSignal.update((count) => count + 1);
 	}
 }