Recognise new IPv6 non-global range from IETF RFC 9602 This PR adds the `5f00::/16` range defined by [IETF RFC 9602](https://datatracker.ietf.org/doc/rfc9602/) to those ranges which `Ipv6Addr::is_global` recognises as a non-global IP. This range is used for Segment Routing (SRv6) SIDs. See also: https://www.iana.org/assignments/iana-ipv6-special-registry/iana-ipv6-special-registry.xhtml Unstable tracking issue: #27709