IIIF: Add CantaloupeProxy class (v10 / for RDM12)

[dfdan]

❤️ Thank you for your contribution!

Description

Backport #2074 for RDM12 to add CantaloupeProxy class.

Checklist

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• I'm aware of the code of conduct.
• I've created logical separate commits and followed the commit message format.
• I've added relevant test cases.
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[github-actions]

This PR was automatically marked as stale.