[mjanthony819]

ru_inn() currently accepts non-ASCII decimal digits because int() converts them to the same numbers as ASCII digits. For example, translating the existing valid company and individual INN examples into fullwidth or Arabic-Indic digits still returns True.

Require an ASCII decimal string before running the existing length and checksum logic. This extends the character-set restriction already applied to Spanish identifiers in #519 and Finnish, French and Indian identifiers in #532. Neither checksum algorithm changes, including the two-check-digit fix in #525.

Ten new regression cases fail before the change and pass afterward. They cover company and individual INNs translated into Arabic-Indic, fullwidth and Devanagari digits, plus single-character substitutions in the first and final positions. The ASCII originals remain accepted.

Validation on Python 3.12:

• All 1,526 configured tests and doctests pass.
• Repository-wide Ruff lint and formatting checks pass.
• Strict Pyright passes with zero errors and warnings using the test environment explicitly.
• git diff --check passes.

AI assistance covered research, implementation, tests and this description.