`cargo doc -p vgi` under `-D warnings` (the CI doc gate) flagged an unresolved
`[finalize]` link and a public->private link on `arg_type_to_arrow_pub`. Point
the first at `Self::finalize`; demote the second to plain code.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>