Add Temporal.ZonedDateTime tests

[robobun]

What does this PR do?

Adds tests for Temporal.ZonedDateTime and the Temporal.Now.{zonedDateTimeISO,plainDateISO,plainTimeISO,plainDateTimeISO} functions.

Blocked on oven-sh/WebKit#218 — these tests exercise the JSC implementation added there. They will fail in CI until that PR is merged and the WebKit hash is bumped. Opening as a draft so the tests are ready to land alongside the bump.

Part of #15853.

How did you verify your code works?

Built locally with --profile=debug-local against the WebKit branch:

test/js/web/temporal/temporal-zoneddatetime.test.ts:
(pass) Temporal.ZonedDateTime exists
(pass) Temporal.ZonedDateTime constructor + getters at Unix epoch in UTC
(pass) Temporal.ZonedDateTime offset time zone
(pass) Temporal.ZonedDateTime named IANA zone honors DST
(pass) Temporal.ZonedDateTime conversions
(pass) Temporal.ZonedDateTime negative epoch (sub-nanosecond boundary)
(pass) Temporal.ZonedDateTime.compare and equals
(pass) Temporal.ZonedDateTime error handling
(pass) Temporal.Now additions (zonedDateTimeISO/plainDateISO/plainTimeISO/plainDateTimeISO)
(pass) Temporal.Instant.from accepts ZonedDateTime
 10 pass  0 fail

All 10 tests fail against current prebuilt WebKit (Temporal.ZonedDateTime is undefined).

[robobun]

^{Updated 5:08 PM PT - May 5th, 2026}

❌ @robobun, your commit e064ec3 has 1 failures in Build #51916 (All Failures):

• test/js/bun/test/parallel/test-http-should-emit-close-when-connection-is-aborted.ts - timeout on 🪟 2019 x64-baseline
• test/js/bun/test/parallel/test-http-should-emit-close-when-connection-is-aborted.ts - timeout on 🪟 2019 x64
• test/js/bun/test/parallel/test-http-should-emit-close-when-connection-is-aborted.ts - timeout on 🪟 11 aarch64

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🧪   To try this PR locally:

bunx bun-pr 30296

That installs a local version of the PR into your bun-30296 executable, so you can run:

bun-30296 --bun

[robobun]

Closing this draft. The Temporal.ZonedDateTime implementation lives entirely in JavaScriptCore — see the stacked PRs on oven-sh/WebKit:

• [Temporal] Implement ZonedDateTime foundation + Temporal.Now additions WebKit#218 — ZonedDateTime foundation + Temporal.Now additions
• [Temporal] ZonedDateTime disambiguation, property bags, startOfDay/hoursInDay WebKit#219 — DST disambiguation, property bags, startOfDay/hoursInDay
• [Temporal] ZonedDateTime add/subtract/with/withPlainTime/withCalendar + PlainDateTime.toZonedDateTime WebKit#220 — add/subtract/with/withPlainTime/withCalendar + PlainDateTime.toZonedDateTime

This Bun PR contained only test/** with no src/** change, so there is nothing for the test-proof gate to validate against, and CI is red only from pre-existing failures on main (oxlint in src/js/internal/sql/errors.ts, test-http-should-emit-close-when-connection-is-aborted.ts timeout on Windows) — the temporal test itself ran cleanly (10 skip / 0 fail).

These tests are preserved on branch farm/65bfe965/temporal-zoneddatetime and should land in the PR that bumps the WebKit hash once the WebKit stack merges. Coverage in the meantime is provided by JSTests/stress/temporal-zoneddatetime.js in the WebKit PRs.

Part of #15853.