Bug: Audio metadata freezes temporarily on webDAV drives

### Description

If the user browses a webDAV mounted to a drive, and the user browses a remote folder with audio files that have metadata like artist, cover image, etc., then the UI freezes for quite a long time. It does not freeze indefinitely, but this degrades the user experience. Ideally, this metadata downloading should be on a separate thread.

### Steps To Reproduce

1. Mount a webDAV drive to the computer (for example, from a nextcloud instance)
2. Browse to a location on the webDAV with multiple audio tracks with metadata
3. The program freezes while it loads the metadata.

### Files Version

4.2.9.0

### Windows Version

10.0.28000.2804

### User ID

24fbe02f-010d-48fa-af4e-261e5301354d

### Log File

[debug.log](https://github.com/user-attachments/files/31970628/debug.log)

Use the reproduction steps and attached debug.log as the starting point; trace audio metadata loading while browsing a WebDAV-mounted folder. Confirm that the UI remains responsive during metadata retrieval, and verify that artist and cover metadata still appears correctly after loading.

Written by the indexing model from the issue text.