feat(isPostalCode): add NG locale

[Adeniyikayodee]

Adds Nigeria to isPostalCode.

On 1 October 2026 Nigeria launched the National Digital Alphanumeric Postcode System (NDAPS), which gives every building an 11-character code: state (2 letters), LGA (2 digits, 01 to 99), district (3 letters or digits), area (2 letters), and building unit (2 digits, 01 to 99). It is written with hyphens (EK-01-A03-FK-01), with spaces (EK 01 A03 FK 01), or compact (EK01A03FK01), in either case.

The rule also accepts the six-digit postal code that came before it, which is still in circulation.

References

• Format specification: https://docs.postcode.gov.ng/concepts/postcode-format
• NIPOST's postcode site: https://postcode.gov.ng/
• Government announcement: https://fmcide.gov.ng/federal-government-launches-national-digital-alphanumeric-postcode-system/
• The same rule in postcode-validator: fix: accept Nigeria's new 11-character postcode melwynfurtado/postcode-validator#302

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable)
• Tests written (where applicable)
• References provided in PR (where applicable)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (9ff3424) to head (c2e8114).

Additional details and impacted files

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  Coverage   100.00%   100.00%           
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  Files          114       114           
  Lines         2599      2599           
  Branches       658       658           
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  Hits          2599      2599           

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