Test UnknownArrayHandle behavior on special arrays
`UnknownArrayHandle` has special behavior when putting in or getting out an `ArrayHandleMultiplexer` or an `ArrayHandleCast`. When putting in either of these, `UnknownArrayHandle` gets the actual array stored in the multiplexer and cast so that you can later retrieve the base array. Likewise, when you get the array out with `AsArrayHandle`, you can give it an `ArrayHandleCast` or `ArrayHandleMultiplexer`, and you will get the base array placed inside of it.
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