[GeoffreyRdn]

Summary

• Add JapanCorporateNumberChecksum for 13 ASCII digits, with the first digit checked against the alternating-weight modulo-9 formula.
• Reuse get_next_digit and keep checksum tests in the validator module.
• Cover official NTA examples, every remainder, invalid check digits, and malformed inputs.

Sources

• NTA formula
• NTA worked example
• NTA API sample

Validation

• cargo test --lib --all-features: 507 passed.
• cargo fmt --all -- --check: passed.
• Strict Clippy: 24 existing diagnostics, identical on unchanged main.

Shared-rule wiring follows after the core release/dependency bump.

Jira: https://datadoghq.atlassian.net/browse/SDS-3138

[datadog-prod-us1-5]

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