NimbleClip 1.13.0

• YouTube audio downloads are much faster: a five-minute song arrives in a
  few seconds where it took two and a half minutes, a four-hour recording in
  under a minute. Pause keeps what has arrived, and a download cut off by the
  app closing is finished the next time it opens. Tried on Android; iOS runs
  the same code and has not been tried on a device.
• Downloads are finished while the app is in the background, on Android.
  The transfers themselves always carried on; what followed them did not
  when Android froze or ended the app: joining the parts of an HD video,
  converting audio to MP3, a stream fetched segment by segment, a slideshow.
  While any download is running NimbleClip now shows a notification
  ("NimbleClip is downloading") and the system leaves it working. The
  notification goes a few seconds after the last
  download ends. Swiping the app away still stops it.
• The repository builds without the private core. dart run tool/use_public_core.dart puts a public core in its place
  (lib/services/extractors_public): one extractor for links to media files
  and for pages with Open Graph metadata, and stand-ins for the rest. Android,
  iOS and Web build from a plain clone that way; the sites NimbleClip knows by
  name still need the full core, which the released builds are made with.
• The platforms are shown by their own marks (YouTube, TikTok, Facebook, X,
  Instagram, Threads, Pinterest, SoundCloud, Flickr) on the home screen, on
  the labels of a result and on the cards of the Downloads screen, where
  stand-in pictures were used before. The marks come from Font Awesome's free
  brand set; its licence is on the Open-source licences page.

What's Changed

• feat(ui): show each platform by its own mark by @vannt-dev in #46
• feat: build without the private core, with a public one in its place by @vannt-dev in #48
• feat: faster YouTube audio downloads, and downloads finished in the background by @vannt-dev in #47
• chore(release): 1.13.0 by @vannt-dev in #49

Full Changelog: v1.12.0...v1.13.0