Login with OTP <= 1.6 - Unauthenticated Authentication Bypass via OTP Brute Force

The Login with OTP plugin for WordPress is vulnerable to authentication bypass in all versions up to, and including, 1.6. This is due to an incomplete fix for CVE-2024-11178: the rate-limit/lockout check added to `otpl_login_action()` was placed only inside the OTP-generation branch and is never evaluated on the OTP-validation branch, and the generated 6-digit OTP additionally has no expiration. This makes it possible for unauthenticated attackers to brute-force the 900,000-value OTP space for any user account (including administrators) and obtain a valid `wp_set_auth_cookie()` session, leading to full site compromise.