feat(cnpj): add alphanumeric CNPJ support (RFB Nota Técnica 49/2024)

[gugacyber]

Summary

Closes #685

Implements support for the new alphanumeric CNPJ format introduced by the Receita Federal do Brasil, effective July 2026 (Nota Técnica Conjunta COCAD/SUARA/RFB nº 49/2024).

Background

Starting July 2026, the RFB will issue CNPJs where the first 12 characters (base + branch) can contain uppercase letters A–Z in addition to digits 0–9. The two check digits (DVs) remain numeric. The validation algorithm is unchanged but character values are computed as ord(char) - 48 instead of int(char).

Changes

File	Change
brutils/cnpj.py	Full alphanumeric support
tests/test_cnpj.py	10 new tests (20 total, all passing)

New helper: _char_value(char)

Converts a character to its RFB numeric value (ord(char) - 48):

• '0'–'9' → 0–9
• 'A'–'Z' → 17–42

Updated: _hashdigit()

Uses _char_value() instead of int() — fully backward compatible.

Updated: validate() / is_valid()

Accept 14-character strings containing [0-9A-Z] with numeric DVs.

Updated: generate()

New alphanumeric=False parameter. Defaults to False for backward compatibility.

from brutils.cnpj import is_valid, format_cnpj, generate

# Canonical RFB example (Nota Técnica 49/2024, Q14)
is_valid('12ABC34501DE35')        # True
format_cnpj('12ABC34501DE35')     # '12.ABC.345/01DE-35'

# Backward compatible
is_valid('03560714000142')        # True
format_cnpj('03560714000142')     # '03.560.714/0001-42'

# Generation
generate()                        # numeric (existing behavior)
generate(alphanumeric=True)       # alphanumeric

Tests

20 passed in 0.72s (10 existing + 10 new)

New test cases:

• Canonical RFB example validates correctly
• Numeric CNPJs remain valid (backward compat)
• Lowercase letters rejected
• Wrong checksum rejected
• All-identical chars rejected
• Alphanumeric formatting
• 50 generated alphanumeric CNPJs all pass validation

[codecov]

Codecov Report

❌ Patch coverage is 92.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.84%. Comparing base (5dc9585) to head (b31c4d3).

Files with missing lines	Patch %	Lines
brutils/cnpj.py	92.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #730      +/-   ##
==========================================
- Coverage   99.08%   98.84%   -0.24%     
==========================================
  Files          26       26              
  Lines         765      782      +17     
==========================================
+ Hits          758      773      +15     
- Misses          7        9       +2     

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[niltonpimentel02]

olá! agradecemos pela sua contribuição, porém, já tem uma pessoa responsável por essa issue e com um pr aberto pra revisão.. por esse motivo esse pr vai ser fechado sem revisão.