feat: add support for alphanumeric CNPJ format

[JeanNesi]

What changes

Adds support for the new alphanumeric CNPJ format (12 uppercase alphanumeric positions + 2 numeric check digits), as defined by the Receita Federal, while keeping the traditional numeric format fully functional.

Examples now accepted:

• 12.ABC.345/01DE-35 (with punctuation)
• 12ABC34501DE35 (without punctuation)
• 00.000.000/0000-00 / 00000000000000 (legacy numeric format)

How

• The check digit calculation now converts each character via its ASCII value offset by 48 ('0' → 0, 'A' → 17), following the Receita Federal spec.
• Validation logic was extracted into two helpers: charToNumber and generateChecksum.
• Normalization now strips only the separators (., /, -), and validation uses the regex ^[A-Z\d]{12}\d{2}$, ensuring uppercase letters in the first 12 positions and numeric digits in the 2 check positions.

Tests

Coverage added in validateCNPJ.spec.ts and usevalidationsbr.spec.ts:

• Valid and invalid alphanumeric CNPJs
• Repeated characters (e.g. BB.BBB.BBB/BBBB-BB, AAAAAAAAAAAAAA)
• Incorrect lengths (shorter and longer than expected)
• Lowercase letters and non-numeric check digits being rejected

All tests pass with pnpm test.

[Guiroos]

Nice implementation of the alphanumeric support!
Followed the patterns of the project and did a good job with the description. Hope that this will be approved 🙏🏻

[AZagatti]

Thank you very much for this, @JeanNesi! 🙏

I reviewed all three alphanumeric-CNPJ PRs against the official Receita Federal reference implementation, and yours was selected as the base: it was the only one using the correct ASCII offset of 48 ('0'→0, 'A'→17). The clean charToNumber / generateChecksum split also fit the codebase nicely (it mirrors validatePIS).

The main branch moved a lot since you opened this (migration to pnpm 11, Biome/ultracite, dependency updates), so rather than merge this branch directly I consolidated your implementation into a fresh PR on top of the current main, adapted it to Biome, and added the full canonical test set from the official reference (including the discriminating 00000000000191 → valid case).

Merged in #67 with you as co-author. Closing this in favor of that PR — thanks again for the great work!

[AZagatti]

Consolidated and merged via #67 (you are credited as co-author). Thank you!

[JeanNesi]

Thank you for the detailed review and for carrying this forward! I'm glad the implementation was useful and that it could serve as the basis for the final solution. I really appreciate the co-author credit and the effort to adapt everything to the current codebase. 🚀