fix: refuse an ipv6 scope id, and say why a value was refused

Four holes of one class, all in the path that admits a query.

ipaddress.ip_address accepts a scope id since Python 3.9, so
"fe80::1%victim@example.org" passed _is_ip, is_queryable returned on
that branch without inspecting the string further, and rdap.query_ip
interpolated the whole thing into the query URL unquoted. A recipient
identifier reached a registry, which is exactly the disclosure the
fourth property exists to prevent and exactly what the domain-branch
fix closed. Reject a scope id at the admission point. fe80::/10 is
link-local and never a legitimate RDAP target anyway.

The ip branch of worklist() dropped an unparseable value silently
rather than funnelling it through add() like the other two branches,
so a mangled indicator vanished from the manifest instead of showing
up as unusable. It now goes through add(), and is_queryable grew the
check that makes that classification correct: an all-digit last label
is never a TLD, so "999.999.999.999" is a malformed IP rather than a
host to ask a registry about.

Two behaviours had no test and both mutations survived. _host_of's
root-dot strip is now covered through the url branch, since failing to
fold discloses one host to a registry twice; the .lower() half was
dead work because urlsplit already lowercases, and is dropped with a
comment saying so. The two-label requirement is asserted on
is_queryable directly, because a single-label name matches no tld in
the bootstrap and a resolve test could never fail whatever the
validator decides.

The refusal message named no reason, leaving a reviewer unable to tell
whether the parser mangled a legitimate host or the attacker planted
something. Two cases now: a non-ASCII name is plausibly a real IDN
indicator to chase by hand, an illegal character is hostile.

Also let KeyboardInterrupt and SystemExit through resolve()'s handler,
so stopping a long run is not recorded as a failed query on whichever
indicator was in flight.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Wrfqr2xqQfhtXCscU7zrdz

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