The previous commit added a recursive re-check of the IPv4 embedded in
NAT64/6to4/Teredo addresses, but the `or` in `blocked-address?`
short-circuits on the truthy keyword returned by `transition-prefix`,
so the embedded-IPv4 branch was unreachable. The transition ranges are
already rejected outright (fail-closed), making the re-check both
unnecessary and untested.
Remove `transition-embedded-ipv4`, simplify the IPv6 branch to a plain
prefix check, and correct the docstrings and tests to match what the
code actually does.
AI-assisted-by: x-preview-f-free
4849e1696c