- wo_ecdsa_p256_sha256_verify: NIST P-256 signature verify for EC-cert chains
and TLS 1.3 CertificateVerify
- Jacobian point arithmetic (double a=-3, general add with the H==0 special
cases), double-and-add scalar mult; field/scalar arithmetic reuses the
bignum Montgomery multiply and modexp (Fermat inverses mod p and mod n)
- validates r,s in [1,n-1] and that Q is on the curve (invalid-curve guard)
- verify-only public data -> not constant-time by design
- renamed the P-256 field mul to fpmul to avoid the clash with X25519's fmul
- VERIFIED against a python ECDSA-P256 vector; tamper + wrong-hash rejected;
test_crypto 69/0; ASan/UBSan clean; battery green
- phase D COMPLETE (RSA PKCS1+PSS + ECDSA-P256). Next E: ASN.1/X.509
(cherry picked from commit 92c996ba96d785d098c173d4ac6ace9052ef6a2f)