Improve app robustness for syncing large shopping lists

[Sietze111]

Description
The app currently struggles when attempting to sync shopping lists containing a large number of items (e.g., in the order of magnitude of 10,000 items). While such a scenario is highly unrealistic for a typical user, enhancing the app to handle this gracefully would improve its robustness and reliability.

Steps to Reproduce
Create or import a shopping list containing approximately 10,000 items.
(I have implemented an import feature in a local branch)
Attempt to sync the list across devices or with the server.

Expected Behavior
The app should handle the synchronization efficiently without errors or performance degradation, even for large lists.

Actual Behavior
The app experiences issues such as slow performance, incomplete syncing, or crashes when handling large lists.

Proposed Solutions
Optimize the synchronization process to handle large datasets more effectively.
Implement batching or chunking for data transfer to prevent overload.
Add error handling and feedback to inform users if a list is too large to sync.