Stabilize ML-DSA X.509 APIs

[vcsjones]

ML-DSA X.509 was recently published as RFC 9881.

We should

• Verify that there are no changes we need to react to compared to the drafts that were used for implementation
• Update test vectors to use the latest if they differ from the draft
• Remove the SYSLIB5006 diagnostic where applicable
• Update any links from draft specifications to the final one

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