Jingle Thief Phishing URL with Embedded Credentials Syntax

Detects URLs that use the `https://user@host` syntax where the 'user' part is crafted to look like a legitimate domain (e.g., `https://example.com@malicious-site.net`). This is a technique used by the Jingle Thief group (also tracked as Atlas Lion and STORM-0539) to craft convincing phishing links.