Add an ignore_errors setting to the yt-dlp archiver, enabled by default.
It passes --ignore-errors so a failed subtitle or thumbnail download no
longer stops yt-dlp before the video download. A non-zero exit is
accepted when a media file exists; the WARNING and ERROR lines are
logged instead of failing the archival.
Per-format streams left by a failed merge (title.f400.mp4) do not count
as media, so a video without its audio stream still fails.
--no-warnings is no longer passed to the download, so failure messages
include the yt-dlp warnings that explain them.