Add unit tests for BaseHyphenatedIdentifierValidator

[JasonWang-0401]

Summary

BaseHyphenatedIdentifierValidator is the abstract base class that implements the shared
framework for OpenMRS's "hyphenated check-digit" patient identifier validators
(LuhnIdentifierValidator, VerhoeffIdentifierValidator). It had no direct unit test —
its behaviour was only exercised indirectly through the two subclass tests, where it is
entangled with each subclass's own check-digit algorithm. (LuhnIdentifierValidatorTest
even carries a // TODO split this into multiple tests note on its single validation method.)

What this adds

A new test, BaseHyphenatedIdentifierValidatorTest, that uses a tiny stub subclass with a
fixed, caller-controlled check digit so the base-class contract can be verified in isolation,
independent of any real check-digit math:

• getValidIdentifier appends - + the correct check letter (the full 0→A … 9→J
  mapping), and uses X as the check character for an out-of-range digit.
• isValid returns true/false correctly, accepts the check letter case-insensitively,
  and works whether the check digit is supplied as a letter (id-D) or an integer (id-3).
• Malformed input throws UnallowedIdentifierException: no hyphen, a trailing hyphen, a
  multi-character check digit (id-10), and a check character that is neither A–J nor a
  digit (id-K).
• The allowed-character rules are enforced: null, empty, whitespace, and disallowed
  characters are all rejected.

The test doubles as living documentation of what a valid hyphenated identifier looks like,
in one place and independent of the Luhn/Verhoeff algorithms.

Testing

./mvnw -pl api test -Dtest=BaseHyphenatedIdentifierValidatorTest

→ Tests run: 10, Failures: 0, Errors: 0, Skipped: 0 — BUILD SUCCESS.

Pure JUnit 5 unit test; no Spring context and no database.

🤖 Generated with Claude Code

[JasonWang-0401]

Superseded by the upstream PR openmrs#6124 (same commit, opened against the official repository).