feat(isMobilePhone): add Vanuatu (bi-VU, en-VU) mobile phone validation

[Code-Breaker-Ctrl]

Summary of Changes

Adds mobile phone validation support and unit test suites for Vanuatu (bi-VU and en-VU).

Closes #1761

Details

• Country Code: +678
• National Significant Number (NSN) Length: 7 digits
• Allocated Mobile Ranges (ITU-T E.164 / TRBR):
  • Digicel Vanuatu: 50–59 (5xxxxxx)
  • Telecom Vanuatu (TVL) / Vodafone: 70–77 (7xxxxxx) and 80–89 (8xxxxxx)
• Files Modified:
  • src/lib/isMobilePhone.js: added regex matcher and en-VU alias.
  • test/validators.test.js: added test cases for bi-VU and en-VU.
  • README.md: updated supported locales documentation.

Verification

• Ran npm test locally:
  • All 323 test suites passing.
  • ESLint checks passing with 0 warnings/errors.D

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (9ff3424) to head (ae9a790).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2931   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          114       114           
  Lines         2599      2600    +1     
  Branches       658       658           
=========================================
+ Hits          2599      2600    +1     

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