feat(registry): add AES-SIV AEAD variant (RFC 5297)

[Mehrn0ush]

As discussed in ticket #763, this PR adds AES-SIV (RFC 5297) as an AEAD variant to the Cryptography Registry.

Fixes #763

Details

• Adds AES[-(128|192|256)]-SIV as an ae variant under the existing AES family.
• Adds authoritative standards reference for RFC 5297.
• Registry-only change (schema/cryptography-defs.json). No schema or specification behavior changes.

[stevespringett]

@bhess

[bhess]

LGTM

[Copilot]

Pull request overview

This PR adds AES-SIV (Synthetic Initialization Vector) as a new AEAD variant to the cryptography registry, addressing issue #763. AES-SIV is defined in RFC 5297 and provides deterministic authenticated encryption with associated data (AEAD).

Changes:

• Adds AES-SIV variant with support for 128, 192, and 256-bit key sizes
• Includes authoritative RFC 5297 standard reference with DOI URL
• Classified as an authenticated encryption (ae) primitive within the AES algorithm family

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[Copilot]

The RFC naming format is inconsistent with most other RFC references in this file. The majority of RFC references use no space (e.g., 'RFC5649' at line 354, 'RFC5869' at line 375, 'RFC8017', 'RFC2104'), while this uses 'RFC 5297' with a space. Although this matches the nearby 'RFC 5116' and 'RFC 3610' references within the AES family, consider using the more common format 'RFC5297' without a space for consistency across the entire file.

Suggested change

	"name": "RFC 5297",
	"name": "RFC5297",