Switch retrieval server delegation cache to ARC cache

[alanshaw]

From #48 (comment)

[hannahhoward]

This issue has been automatically moved to Stuck / Dead Issue status.

Reason: No activity for 180 days (threshold: 180 days)

If this issue is still relevant and you'd like to work on it, please:

1. Comment on this issue with an update
2. Move it back to Backlog or another appropriate status
3. Consider if this should be moved to Icebox instead

---

Automated by project-agent