feat: add support for alphanumeric CNPJ format (effective July 2026)

[easedu]

Description

This PR implements support for the upcoming alphanumeric CNPJ format (effective July 2026) for Brazilian tax IDs, as described in issue #2639.

Starting July 2026, Brazil's Receita Federal will support alphanumeric CNPJs with the same structure as numeric CNPJs but allowing letters A-Z in addition to digits 0-9.

Changes

• Update ptBrCheck function in src/lib/isTaxID.js to validate both numeric and alphanumeric CNPJs
• Add character-to-value conversion (A-Z → 17-42) following the formula: ASCII code - 48
• Maintain backward compatibility with numeric-only CNPJs
• Add comprehensive tests for both formats including:
  • Existing numeric CNPJs (backward compatibility)
  • New alphanumeric CNPJs (including official example 12.ABC.345/01DE-35)
  • Invalid CNPJs in both formats
  • Formatted and unformatted inputs

References

• Official SERPRO documentation: Cálculo dos dígitos verificadores de CNPJ alfanumérico (PDF provided by the Brazilian government detailing the complete validation algorithm)
• Receita Federal announcement: CNPJ Alfanumérico

The validation algorithm uses:

• Module 11 check digit calculation
• Weights from 2 to 9 (right to left, repeating after 8th character)
• Character conversion: digits 0-9 remain as is, letters A-Z convert to values 17-42
• Check digit rule: if remainder = 0 or 1 → DV = 0, else → DV = 11 - remainder

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable) - Not applicable: no user-facing documentation changes needed
• Tests written (where applicable)
• References provided in PR (where applicable)

Closes #2639

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (784e52a) to head (d109441).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2644   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          114       114           
  Lines         2572      2574    +2     
  Branches       651       650    -1     
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+ Hits          2572      2574    +2     

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