How does stalePeriod work?

I passed a `cacheManager` to the `CachedNetworkImage` widget we are using.

To test whether the image is deleted from the cache or not, I set the `stalePeriod` to 5 seconds. Like this:

```dart
CachedNetworkImage(
imageUrl: "myimagelink"
cacheManager: CustomCacheManager.instance,
),

// ...

class CustomCacheManager {
static const key = DefaultCacheManager.key;
static CacheManager instance = CacheManager(
Config(
key,
stalePeriod: const Duration(seconds: 5),
),
);
}
```

However, the cache manager is not working as expected. If an image is cached and then not used for 5 seconds, shouldn't it be automatically deleted from the cache? We believe it should work this way. Or do we need to delete it manually?