Closes #638

What

US.yaml had Mardi Gras (easter -47) under LA.regions.NO, so US-LA did not return it at all — only US-LA-NO did. Mardi Gras is not a New Orleans-only holiday:

• R.S. 1:55 B(1)(a) — state employees shall not work on Mardi Gras Day, so state offices close state-wide. This matches the state holiday calendar linked in the issue.
• R.S. 1:55 A(3) — Mardi Gras is a legal holiday in the 29 listed parishes (Orleans, Jefferson, East Baton Rouge, Lafayette, …) once the parish governing authority declares it by ordinance, and in all municipalities.

Source: https://legis.la.gov/Legis/Law.aspx?d=74097

State level is the closest fit for this library's granularity, so easter -47 moves to LA.days with the statute cited in a comment.

Two deliberate scope decisions

1. regions.NO is kept (name only). Dropping it would remove NO from getRegions('US', 'LA') and break existing US-LA-NO lookups. Keeping the region means Mardi Gras reaches New Orleans by inheritance, so nothing regresses and the US-LA-NO-* fixtures stay byte-identical.
2. Lundi Gras is not added. The issue says the day before is "apparently" a holiday too, but R.S. 1:55 does not mention the Monday before Mardi Gras, so I left it out rather than guess. Happy to add it if you have a source.

Verification

• npm run yaml — clean
• npm test — 5373 passing
• npm run lint — clean
• Fixtures regenerated with the project tool: mocha test/all.mocha.js --writetests --countries US → only test/fixtures/US-LA-2015..2029.json change, one Mardi Gras entry each (US-LA-NO-* unchanged, as expected)
• Runtime check for 2026: US-LA → 2026-02-17 Mardi Gras, US-LA-NO → same, US-TX unaffected, getRegions('US','LA') → {"NO":"New Orleans"}

_{Independently cross-reviewed by two AI models before submission.}