fix(isPassportNumber): support case-insensitive country codes

[smoelius]

fix(isPassportNumber): support case-insensitive country codes

This PR fixes a TypeError in isPassportNumber when a lowercase or mixed-case country code is provided.

Previously, the validator checked the normalized uppercase country code but accessed the passport regex map using the original country code. The country code is now normalized once and used consistently for both operations.

Regression tests cover lowercase (am) and mixed-case (aM) country codes with valid and invalid Armenian passport numbers.

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 (ce62eb4) to head (bdb2ac7).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2821   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          114       114           
  Lines         2587      2588    +1     
  Branches       656       656           
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+ Hits          2587      2588    +1     

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[tux-tn]

ISO 3166-1 alpha-2 defines two-letter country codes in uppercase letters. I think lower or mixed case letters shouldn't be considered valid ISO 3166-1 codes.

5.1 Code element formation
Code element shall consist only of the following characters (cf. ISO/IEC 10646):
— LATIN CAPITAL LETTER A through LATIN CAPITAL LETTER Z