DownloadGifUseCase
interface DownloadGifUseCase
Downloads a GIF's Gif.original rendition from Giphy's CDN to a temporary file. Fails if the response isn't a GIF file (GIF87a or GIF89a header), so nothing else is sent as image/gif. Show that file as the preview and pass it to SendGifMessageUseCase, so the GIF is downloaded only once.