The movie/show/season/episode/artist/album/track to 1/2/3/4/8/9/10 table
was repeated in the query translator (forward and inverse), collection
creation, and the metadata-edit adapter; PlexMetadataType now owns
forKind/kindFor and each caller keeps its own unsupported sentinel.
getMetadataWithImagesAndOnDeck and _getMetadataWithImages shared the
endpoint, cache key, query flags, first-row parsing, and library-section
stamping and differed only by includeOnDeck; they are one private typed
fetcher returning (metadata, onDeckEpisode), so fetchItemWithOnDeck no
longer reads a string-keyed dynamic map.
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