New Extractor Idea: `podcast-archiver` for auto-downloading podcasts

https://github.com/janw/podcast-archiver

Podcast Archiver takes the feed URLs of your favorite podcasts and downloads all available episodes for you—even those "hidden" in [paged feeds](https://podlove.org/paged-feeds/). You'll end up with a complete archive of your shows. The archiver also supports updating an existing archive, so that it lends itself to be set up as a cronjob.

```bash
pipx install podcast-archiver

podcast-archiver -d ~/Music/Podcasts \
-f http://logbuch-netzpolitik.de/feed/m4a \
-f http://raumzeit-podcast.de/feed/m4a/ \
-f https://feeds.lagedernation.org/feeds/ldn-mp3.xml
```

Review the linked podcast-archiver project and the existing extractor conventions in abx-plugins first. Use the example command and requirements as acceptance criteria: feed URLs should produce a complete episode archive, including paged feeds, and rerunning the extractor should update an existing archive.

Written by the indexing model from the issue text.