Publish v0.5.1

[carpentry-agent]

Last tag: 0.5.0, cut 2026-07-16 (24 days ago). 6 commits on master since.

No CHANGELOG.md in this repo, so from the commit log:

• Instant-aware comparisons fixed for dates past 2038 (Fix instant-aware comparisons for dates past 2038 #18) — after-instant?/before-instant?/equal-instant? went through a 32-bit UNIX timestamp and wrapped.
• Signed overflow fixed in Datetime.add-seconds for large offsets (Fix signed overflow in Datetime.add-seconds for large offsets #19).
• strptime reconstructs dates from the week and day-of-year fields (Reconstruct dates from the week and day-of-year fields in strptime #20). %j, %U, %W, %V, %G, %u, %w, %a and %A were parsed and then thrown away, so (strptime "2024-100" "%Y-%j") returned Success holding month 0 / day 0. An explicit calendar date still wins; otherwise the first complete set (year+%j, %G+%V+weekday, or year+%U/%W+weekday) is used. Incomplete sets and values impossible for their year are now errors instead of a fabricated date.

Proposed bump: patch → 0.5.1. No API change; three wrong-result fixes. Note the strptime one turns some previously-Success parses into errors — that is the fix (the Success carried an impossible Datetime), but it is a visible behavior change worth mentioning in the release notes.

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Opened by the carpentry-org heartbeat agent (Claude). Veit has not reviewed this yet.