fix: reject offset on a bare local time or date

[hong4rc]

Issue

parse() accepts a TOML time-of-day or date that carries a timezone offset (Z or ±HH:MM) and silently corrupts the value instead of rejecting it. Per TOML, an offset is only valid on an offset-date-time (a full date and time); local-time, local-date, and local-date-time have no offset.

opens = 08:30:00-07:00   # accepted, parsed as 15:30 (shifted to UTC) — not rejected
t     = 07:32:00Z        # accepted, Z silently dropped → 07:32 local
d     = 1979-05-27Z      # accepted, Z silently dropped

Input	Current	Expected (TOML 1.0)
08:30:00-07:00	accepted → 15:30:00 (corrupted)	error — offset not allowed on a local time
07:32:00Z	accepted → 07:32:00 (Z dropped)	error
1979-05-27Z	accepted → 1979-05-27 (Z dropped)	error
1979-05-27T07:32:00-07:00	accepted (correct)	valid offset-date-time
07:32:00 / 1979-05-27	accepted (correct)	valid local-time / local-date

Why it happens

In TomlDate's constructor (src/date.ts), the offset capture group (match[3]) is applied whenever it's present, with no check that a date (match[1]) and a time (match[2]) accompany it. super(...) then builds a valid Date shifted to UTC, but the value is classified as a local time/date, so reading it back yields the UTC-shifted instant — a silently wrong value, and an invalid construct accepted.

Fix

Reject an offset that isn't on a full date-time — match[3] present while match[1] (date) or match[2] (time) is missing — alongside the existing rollover-hours guard. Offset-date-times and bare local-time/local-date are unaffected.

Tests

Added 07:32:00Z, 07:32:00-07:00, and 1979-05-27Z to the "rejects invalid dates" suite. Full suite passes (141 tests).