fix(dsa): reject invalid domain parameters to prevent universal signature forgery

[Kr0emer]

Summary

This PR fixes a high-impact DSA verification issue caused by missing domain-parameter validation.

Without validation, attacker-controlled DSA parameters (e.g. g=1, y=1) can make verification accept a forged signature for arbitrary message hashes.

Root Cause

KJUR.crypto.DSA accepted public parameters without checking DSA domain/public key constraints.
As a result, verification could be performed on invalid groups/keys.

Changes

• src/dsa-2.0.js
  • add strict validation in public key import path (setPublic):
    • 1 < q < p
    • 1 < g < p
    • g^q mod p == 1
    • 1 < y < p
  • reject invalid keys with Error: invalid DSA public key
• test/qunit-do-dsa.html
  • add regression: setPublicHex rejects g=1
• test/qunit-do-x509.html
  • add regression: forged self-signed DSA certificate with g=1 is rejected by X509.verifySignature

Security Impact

Prevents universal DSA signature forgery under malicious parameters and blocks forged-certificate acceptance in DSA verification flows that consume untrusted keys/certs.

Validation

• Reproduced vulnerable behavior before fix using PoC (g=1): forged signature/cert accepted.
• After fix: invalid key rejected (invalid DSA public key), forged verification fails.
• npm test in npm/ passes.