Fix NG NIN rejecting valid numbers with a leading zero

[jichaowang02-lang]

Change Description

NgNinRecognizer validated the Verhoeff checksum on int(value):

def __check_nin(self, value: str) -> bool:
    return (
        len(value) == 11
        and value.isnumeric()
        and self._is_verhoeff_number(int(value))   # int() drops a leading zero
    )

int("00000000005") → 5, and _is_verhoeff_number then runs str(...) on it, so the checksum is computed on a shortened digit string. An 11‑digit NIN that begins with 0 — e.g. 00000000005, a genuinely valid Verhoeff number — is checked on fewer than 11 digits and wrongly rejected (a false negative for the ~10% of the NIN space that starts with 0). The NIN spec places no restriction forbidding a leading zero.

Fix

Pass the digit string to the Verhoeff check instead of int(value), so all 11 digits are validated. Non‑leading‑zero NINs are unaffected.

Checklist

• I have reviewed the contribution guidelines
• I have added tests to cover my changes
• All new and existing tests passed

Tests

$ pytest tests/test_ng_nin_recognizer.py -q
14 passed

• New analyze-level case for a leading-zero NIN (VALID_NIN_LEADING_ZERO) — fails before the fix, passes after.
• New direct Verhoeff regression asserting a leading-zero NIN is accepted.
• Corrected the prior all-zeros unit test: it passed int(0) — a single "0", which is a valid Verhoeff number — rather than the 11-digit all-zero string (which is not valid), so it never exercised the all-zero NIN.

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