GHSA-wppf-h75h-6pm6: SearXNG MCP Server: Additional hardened-mode SSRF bypasses

The mcp-searxng server has a feature in hardened mode that tries to prevent SSRF (server-side request forgery, where an attacker tricks a server into fetching URLs it shouldn't) attacks on the web_url_read function. However, three bypasses still exist: redirects from allowed URLs to internal addresses aren't re-checked, the address 0.0.0.0 isn't blocked as internal, and IPv6-mapped IPv4 addresses can bypass checks after the URL parser converts them to a different format.