Implement incremental/partial fetch #104
Description
When a file is changed remotely, the Nextcloud desktop client will retrieve the entirety of the changed file's contents. However, there are more efficient ways to handle file change retrieval.
The File Provider API provides some method to acquire partial contents of a file. However, the server does not provide a mechanism at this time to provide the specific parts of a file that have changed.
Your task is to implement an algorithm that can implement this. Ideally you will touch parts of the server and the desktop client, so that other clients may also benefit.