None of these files are necessary to see or to have a cover on an epub in any spec epub reader I have ever used. I read epubs in iBooks/Books all of the time created with Sigil and see covers with no problems. And none of them are listed by the opf manifest. So these are not normal epub files that meet any epub specification.
So what are they?
Have you tried unzipping your epub and looking at them? The .plist files are macOS proprietary xml-like property list files. As for the Artwork, it has no image extension so it could be anything.
So not sure why iOs needs or adds these files but they are not required for an epub to have or show a cover.
You might try running your epub through stanadalone epubcheck to see what it says.
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