Thumbnail Generation For File Listing

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`DisplayUtils.setThumbnail` is currently used to load thumbnails in the file listing, and it is tied to the `onBindViewHolder` method of `OCFileListAdapter`.

However, `setThumbnail` performs multiple checks and triggers asynchronous operations, making it inefficient when called repeatedly during binding.

To improve this, we could introduce a separate component responsible for preparing thumbnails for all files in advance. This component would:

* Preload or generate thumbnails for the entire list after a directory swap
* Update thumbnails for individual files when changes occur

The adapter would then simply display already-prepared thumbnails instead of triggering the full thumbnail logic during each bind.

### Note

Planning needed before implementation