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/i18n/fr.json

@@ -10,6 +10,8 @@
 		"description": "Ajoutez chaque solde de congés et sa période de validité.",
 		"addVacationDay": "Ajouter un solde de congés",
 		"calculate": "Calculer le planning",
+		"durationEstimate": "Attente indicative : {range} {unit}",
+		"durationUnits": { "seconds": "s", "minutes": "min" },
 		"remainingDaysWarning": "{count} jour{plural} de vacances non placé{plural}:",
 		"remainingDaysManualPlace": "Veuillez les placer manuellement.",
 		"deleteEntry": "Supprimer l’entrée",