Adding Background Image Functionality

**Additional context**
the component is very good.But some time,i think backgroundImage is needed more than backgroundColor

The issue is about the LiquidPullToRefresh component. Look at the component's source code to understand how backgroundColor is implemented. Research how to add a backgroundImage property in Flutter widgets, likely involving decoration. Check existing examples or tests in the repository to see the component's usage pattern.

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