Audit non-normative SpiderMonkey staging exclusions and remove or replace them

Context

The configured runner excludes 10 SpiderMonkey staging files before enumeration: 8 Date DST stress probes and 2 stale Annex B arguments cases. These are listed in docs/.data/test262-excluded.tsv as spidermonkey-date-stress and stale-spidermonkey-annex-b.

Current rationale

• The Date files are stress probes that are not useful as ordinary conformance scoring inputs.
• The two Annex B staging cases predate or contradict current official Annex B coverage; the official test262 Annex B coverage is scored and passing.

Done when

• Reconfirm whether each file should remain excluded, be deleted from the local configured surface, or be replaced by current normative coverage.
• If any file should be scored, fix the runtime or timeout behavior and promote it into the runner.
• Keep docs/.data/test262-excluded.tsv and README/docs wording aligned with the final decision.
• zig build test262 stays green.

Completed and pushed in 1fa9e65.\n\nThe staging audit now leaves only 11 non-normative staging files outside the denominator: 8 SpiderMonkey Date DST stress probes, 2 stale Annex-B cases, and 1 strict block-function case marked esid: pending. The previously surfaced staging source-phase-imports case is implemented/scored and passes.\n\nFocused staging run: 0 fail, 1,474 pass with the audited exclusions applied. Full regenerated docs data is green at VALID 48,486/48,486 and NEGATIVE 4,669/4,669. README/docs and docs/.data/test262-excluded.tsv are aligned with the final inventory.