feat(isIdentityCard): add KR(South Korea) locale in validators

[SHINDongHyeo]

isIdentityCard.js

This PR adds a validator for South Korean national identification numbers (주민등록번호, 주민번호).

A South Korean ID number has the format YYMMDD-GXXXXXX:

• YYMMDD: date of birth
• G: gender and century indicator
  • 1 or 2 = born 1900–1999
  • 3 or 4 = born 2000–2099
• The remaining 6 digits (XXXXXX) are random codes.

This validator checks:

• valid date format (YYMMDD)
• correct grouping format with optional hyphen
• valid G digit based on birth year

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 (d91af4b) to head (9f91515).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2558   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          114       114           
  Lines         2535      2543    +8     
  Branches       641       642    +1     
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+ Hits          2535      2543    +8     

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