[karlkauc]

Jira: https://issues.apache.org/jira/browse/VALIDATOR-481

What

• Modulus97CheckDigit: a generic check digit routine for the pure system ISO/IEC 7064, MOD 97-10 with the two numeric check digits at the end of the code. IBANCheckDigit uses the same algorithm, but IBAN check digits sit at positions 3–4 and the code is rearranged first; this class does not rearrange anything, so it works for all MOD 97-10 codes with trailing check digits (LEI, German Leitweg-ID, …). Check values 00, 01 and 99 are rejected, as the calculation can only produce 02–98.
• LEIValidator: validation of Legal Entity Identifiers (ISO 17442), built on CodeValidator with the regex [A-Z0-9]{18}[0-9]{2}, length 20 and the new check digit routine. Same structure as ISINValidator (singleton getInstance(), isValid(), validate()). Characters 5–6 are no longer required to be 00 since ISO 17442-1:2020, so this is not enforced.
• Tests for both classes (Modulus97CheckDigitTest extends AbstractCheckDigitTest), a new section 4.6 "LEI validation" in package-info.java, and a changes.xml entry.

Why

Commons Validator has no LEI support. LEIs are mandatory identifiers in financial regulatory reporting (MiFID II, EMIR, Solvency II, FundsXML, …), and the check digit scheme is a well-defined ISO standard with a single authoritative source (GLEIF), comparable to IBAN and ISIN which are already covered.

Scope

This PR is intentionally small. It picks up the LEI part of the withdrawn #61 and follows the feedback in #271, where the maintainers said that generic, standardised CheckDigit implementations are welcome while country-specific validators with many moving parts are not. No Leitweg-ID or VAT validators are included; the Leitweg-ID example is only used as a test case to show the routine is not LEI-specific.

Differences to the Modulus97CheckDigit proposed in #61: calculate() follows the CheckDigit contract and takes the code without check digits; the validator reuses CodeValidator instead of a custom wrapper; null is checked before trimming; Javadoc documents the standard and the test data sources.

Testing

• The default Maven goal (mvn: verify, apache-rat, japicmp, checkstyle, spotbugs, pmd, javadoc) passes with 3,314 tests.
• Test LEIs come from public GLEIF data (https://search.gleif.org/, including GLEIF's own LEI 5493001KJTIIGC8Y1R12), plus the ISO/IEC 7064 example 794 → 79444 and the Leitweg-ID example 04011000-1234512345-06.
• The routine was additionally cross-checked against IBANCheckDigit (by moving the last four characters to the front) on 10,473 distinct real-world LEIs from FundsXML fund reports: identical results, 10,471 valid, 2 placeholders correctly rejected.

References

• ISO 17442 / LEI structure: https://www.gleif.org/en/about-lei/iso-17442-the-lei-code-structure
• ISO/IEC 7064: https://en.wikipedia.org/wiki/ISO/IEC_7064