- Apply _normalize_addr in _is_allowed_loopback_target so
::ffff:127.0.0.1 is correctly identified as loopback
- Add test for contains_internal_url with IPv6-mapped addresses
- Add test for whitelist + IPv6-mapped CGNAT interaction
::ffff:127.0.0.1 and ::ffff:169.254.169.254 are IPv6Address objects
that match neither the IPv4 blocklists (127.0.0.0/8, 169.254.0.0/16)
nor the IPv6 ones (::1/128), allowing SSRF bypass via DNS responses
that return IPv6-mapped IPv4 addresses.
Add _normalize_addr() to convert ipv4_mapped IPv6 addresses to their
IPv4 form before blocklist/allowlist matching.
