roundtrip/escaping — signed fixture for character-string escaping

First fixture of the *_human() round-trip program: a signed zone whose
records deliberately contain characters that need RFC 1035 escaping in
presentation form — double quotes, backslashes, and non-printable bytes
(escaped as \DDD) — across every type whose rdata carries character-strings:
HINFO, TXT, SPF, WALLET, ISDN (with and without subaddress), X25, and NAPTR
(one with empty regexp and "." replacement, one with a backslash-containing
regexp and a real replacement name).

One TXT segment has a \009 (tab) escape immediately followed by a literal
digit. This is positive regression coverage for the exactly-3-digit \DDD
parse in extract_text(): a greedy (unbounded) digit scan would misread
"\0092" as a single byte and break RRSIG verification for the TXT RRset.
Another TXT segment carries trailing spaces inside the quotes, and one
segment is empty (""). A further segment carries an embedded NUL byte
(\000) surrounded by printable text ("nul\000inside"), proving the
rendering path copies each segment by its stored length rather than
truncating at the first NUL the way a naive %s format would.

The RRSIGs are the canary: any wire-format encoding regression for these
records breaks signature verification immediately. Later-stage tests also
render these records with -v and splice them back into the zone, proving
the *_human() output is wire-identical to the original.

Zone signed with RSASHA256 so signatures validate on every platform
(including RHEL9 where SHA-1 is disabled by crypto policy). Signing window
is 30 days (2027-01-01 .. 2027-01-31 UTC); the fixture is anchored by -t,
so window length does not affect test stability.

Test-time used by src/t/test.pl: 1800057600 (2027-01-16 00:00 UTC,
mid-window). If regenerate.sh is changed to use a different window, update
the -t flag in test.pl accordingly.

To regenerate:

    cd src/t/roundtrip/escaping
    ./regenerate.sh
