pydantic-ai: SSRF blocklist bypass via IPv4-compatible, SIIT/IVI, and local NAT64 IPv6 addresses (incomplete fix of CVE-2026-46678)

Summary When an application using Pydantic AI opts a URL into forcedownload='allow-local' which disables the default block on private/internal IPs and runs on a network that routes the affected IPv6 transition forms NAT64- or ISATAP-configured networks, the cloud-metadata blocklist could be...