Bifrost's SSRF deny-list is incomplete: isPublicIP permits CGNAT, IPv6 6to4/NAT64, and site-local in FetchAndEncodeURL

Summary isPublicIP in core/providers/utils/fetch.go — the SSRF deny-list that gates FetchAndEncodeURL — does not reject several routable address ranges that map onto internal infrastructure. Carrier-Grade NAT 100.64.0.0/10, RFC 6598, IPv6 6to4 2002::/16, NAT64 64:ff9b::/96 and 64:ff9b:1::/48, and...