visa() hardcodes 16 digits although Visa supports 19-digit PANs #556

validators.visa() requires exactly 16 digits, but Visa supports 19-digit PANs. A 19-digit input with Visa's leading 4 and a valid Luhn checksum is rejected solely because of its length.

Reproduced with validators 0.36.0 at current master commit 22786cc6e7283a0fa452c179797e447f798db9f0 on Python 3.14.8:

from validators import card_number, visa

for value in ('4000000000000002', '4000000000000000006'):
    print(value, len(value), repr(card_number(value)), repr(visa(value)))

Observed:

4000000000000002 16 True True
4000000000000000006 19 True ValidationError(func=visa, args={'value': '4000000000000000006'})

These are synthetic structural test values, not issued card accounts. card_number() confirms that both pass the package's generic Luhn check.

Expected: visa() should not reject a Visa-format input just because it has 19 digits. Visa's public Transaction Acceptance Device Guide, section 2.1, discusses variable-length Visa PANs up to 19 digits.

The rejection comes from len(value) == 16 in src/validators/card.py:visa.