fix(isVAT): validate the RO check digit

[vicuts]

isVAT(str, 'RO') only checked that the code has 2 to 10 digits, so any number of that length passed, including codes with a wrong check digit.

Romanian VAT numbers (CUI/CIF) end in a check digit. This adds the standard check, in the same style as the existing AU, CH and PT matchers:

1. Take the digits before the check digit and left-pad them with zeros to 9 digits.
2. Multiply them by the key 753217532 and add the products.
3. Multiply the sum by 10 and take it modulo 11. A remainder of 10 means 0.
4. The result must equal the check digit.

The previous valid examples 1234567890 and 12 have wrong check digits, so they move to the invalid list. RO codes with a wrong check digit that passed before are now rejected, which is the intended fix.

References

• Romanian Wikipedia, "Număr de identificare fiscală": https://ro.wikipedia.org/wiki/Cod_de_identificare_fiscal%C4%83. It describes the key 753217532 and works through 14399840, which is now one of the valid test cases.

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable): no change needed, RO is already listed for isVAT and the API is the same
• 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 (e91b82e).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2900   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          114       114           
  Lines         2599      2608    +9     
  Branches       658       660    +2     
=========================================
+ Hits          2599      2608    +9     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.