fix(registry): correct RFC 3610 DOI reference

[Mehrn0ush]

As discussed in ticket #761, this PR fixes an incorrect standards reference in the Cryptography Registry.

Fixes #761

Details

• Corrects the RFC 3610 DOI under the AES AEAD variant (previously pointed to RFC 5116).
• Registry-only data-quality fix.
• No schema or specification behavior changes.

[stevespringett]

@bhess

[bhess]

Thanks for the fix!
Please remove the "XChaCha20" entry since it overlaps with your other PR. Other than that, LGTM!

[Copilot]

Pull request overview

This PR corrects an incorrect DOI reference in the Cryptography Registry and adds support for the XChaCha20-Poly1305 AEAD cipher variant.

Changes:

• Fixes the RFC 3610 DOI URL (was incorrectly pointing to RFC5116)
• Adds XChaCha20-Poly1305 as a new authenticated encryption variant in the ChaCha20 family

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[Copilot]

The addition of XChaCha20-Poly1305 is not mentioned in the PR description, which states this is a 'Registry-only data-quality fix' for the RFC 3610 DOI. The PR description claims 'No schema or specification behavior changes,' but adding a new cipher variant is a functional change. Either the PR description should be updated to document this addition, or if this change was included unintentionally, it should be moved to a separate PR. Additionally, XChaCha20-Poly1305 should have a standard reference (such as draft-irtf-cfrg-xchacha) similar to how ChaCha20-Poly1305 references RFC8439.