Custom Age Threshold On Cache Objects Over Capacity

## 🏗 Enhancement Proposal

Allow configuring the age threshold used when cleaning up cache objects over capacity.

### Pitch

Currently, `getObjectsOverCapacity` uses a hardcoded `Duration(days: 1)` to filter which cached objects are eligible for removal during cleanup. This means objects touched within the last 24 hours are never removed, even if the cache exceeds its capacity.

This can be problematic in scenarios where:
- Apps have high cache turnover and need more aggressive cleanup (e.g., `Duration(hours: 6)`)
- Apps want to preserve recently accessed items for longer periods (e.g., `Duration(days: 7)`)
- The 1-day threshold doesn't align with the app's usage patterns

**Proposed solution:**

Add an optional `maxCapacityAgeFilterDuration` parameter to `Config` that allows developers to customize this threshold. The parameter defaults to `Duration(days: 1)` to maintain backward compatibility.

```dart
CacheManager(
Config(
'customCacheKey',
maxCapacityAgeFilterDuration: Duration(hours: 12), // Only remove items untouched for 12+ hours
),
);
```

This gives developers fine-grained control over cache eviction behavior without changing the default experience.

### Platforms affected (mark all that apply)
- [x] :iphone: iOS
- [x] :robot: Android

Repérez Config et getObjectsOverCapacity, puis suivez l’endroit où la Duration d’un jour codée en dur est utilisée lors du nettoyage. Ajoutez la Duration facultative tout en conservant la valeur par défaut d’un jour, prenez en charge des valeurs personnalisées telles que 12 heures et vérifiez que le nettoyage du cache respecte toujours le seuil configuré.

Rédigé par le modèle d'indexation à partir du texte de l'issue.