fix(node): support ECDSA with secp256k1 in `node:crypto` (#32390)
## Summary
- Adds secp256k1 ECDSA support to `node:crypto` key generation, signing,
verification, and key import/export (DER, PEM, JWK)
- Adds `Secp256k1` variant to `EcPrivateKey`/`EcPublicKey` enums using
the existing `k256` crate
- Enables `ecdh`, `jwk`, `pem` features on `k256` workspace dependency
Closes #27523
## Details
The `k256` crate was already used for ECDH with secp256k1, but the ECDSA
key generation/signing/verification paths only supported P-224, P-256,
and P-384. This PR adds secp256k1 support across all EC code paths:
- **Key generation**: `generateKeyPair('ec', { namedCurve: 'secp256k1'
})` now works
- **Signing/verification**: `sign()`, `verify()`, `createSign()`,
`createVerify()` with secp256k1 keys
- **Key import/export**: PKCS#8, SEC1, SPKI (DER/PEM), and JWK formats
- **Key details**: Reports `namedCurve: "secp256k1"` in
`asymmetricKeyDetails`
- **X.509**: Parsing secp256k1 public keys from certificates
- **DH**: `diffieHellman()` with secp256k1 KeyObject pairs
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
