crypto/ocsp: add support for Ed25519 signatures in OCSP responses

[Minipada]

This PR is necessary to work with the ocsp server in cfssl.
See additional PR there cloudflare/cfssl#1420

This PR adds support for the EdDSA Ed25519 signature algorithm
to the OCSP response signing logic. This allows cfssl to
generate OCSP responses using Ed25519 keys, in compliance
with RFC 8410.

Key Changes:

• added OID for Ed25519 (1.3.101.112) in oidSignatureEd25519
• updated signingParamsForPublicKey to recognize ed25519.PublicKey, set
  appropriate pkix.AlgorithmIdentifier, and avoid setting Parameters
  (as required by RFC 8410)
• extended signatureAlgorithmDetails to include x509.PureEd25519
• updated CreateResponse to avoid hashing the TBSResponseData when
  crypto.Hash(0) is used (i.e., for Ed25519), passing the raw DER
  directly to priv.Sign
• error messages updated to reflect Ed25519 as a supported key type

Motivation:

Ed25519 is widely adopted due to its performance, small key size, and
resistance to common cryptographic attacks. Supporting it in OCSP
flows is critical for enabling modern PKI infrastructures that
prefer or require Ed25519-based certificates and responders.

Compatibility

This change is backward-compatible. The existing RSA and ECDSA flows
remain untouched. Ed25519 is only engaged if the responder key is of
type ed25519.PublicKey and the SignatureAlgorithm is x509.PureEd25519.

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Message from Gopher Robot:

Patch Set 1:

(1 comment)

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Patch Set 1:

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Message from david bensoussan:

Patch Set 5:

(1 comment)

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