Fix OGRNIP check digits for two-digit remainders

[natesute]

For 15-digit OGRNIP numbers, the check digit is the last decimal digit of the remainder modulo 13. The current calculation returns two characters when the remainder is 10, 11 or 12, rejecting numbers whose final digit is correctly 0, 1 or 2.

Apply the final modulo 10, as the 13-digit OGRN branch already does. Add regression coverage for all three affected remainders, validation of those numbers, and rejection of incorrect check digits. Also correct the OGRNIP test section's length label.

Fixes #516.

Validation: the new doctest fails on the original implementation (['10', '11', '12'] instead of ['0', '1', '2']). The complete suite passes with the fix: 413 passed, 9 skipped, 100% statement and branch coverage. Scoped flake8 passes.