version-bump v3.2.4

[ankitdas13]

Summary

• Bumps version from 3.2.3 → 3.2.4
• Updates CHANGELOG with fix from PR fix: use random nonce per call in AES-GCM onboarding signature #270

Test plan

• Verify Razorpay::VERSION returns 3.2.4
• Confirm generate_onboarding_signature produces output in new format: hex(iv || ciphertext || tag)
• Run full test suite (bundle exec rake)

🤖 Generated with Claude Code

[manikrazorpay13]

LGTM.