feat: Download single WACZ file when possible

[SuaYoo]

Resolves #2648

Changes

Uses sole WACZ file instead of creating new multi-WACZ when downloading an archived item.

Manual testing

1. Log in
2. Go to an archived item with a single WACZ file
3. Go to "Files" tab. Verify "Download File" button is shown
4. Select "Download File". Verify the same WACZ file as the one listed in "WACZ Files" list is downloaded
5. Go to workflow for the archived item
6. Select "Download" from the "Latest Crawl" tab. Verify same single WACZ file is downloaded
7. Regression test for archived item with multiple WACZ files

Screenshots

Page	Image/video
Archived Item / WACZ Files

Follow-ups

"Download Item" in the archived items list still downloads a multi-WACZ file since resources is omitted in the all-crawls response. If we want to enable single WACZ downloads from this view, we could do follow-up work to request the item resources in a separate frontend API call, or the backend could include a download link in the list response data.