Make the 'Index Points' node index within each vector element instead of across the whole list

[Keavon]

This has no migration because avoiding repeated migrations would necessitate leaving behind cruft. I'm deeming this rare enough that users can do the migration manually if encountered: inserting a 'Combine Paths' node before 'Index Points'.

[cubic-dev-ai]

No issues found across 1 file

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Re-trigger cubic}