Anchor VersionMapper to the trailing version segment (#374)

[elharo]

Fixes #374

Summary

VersionMapper.mapFileName had two bugs:

1. When the version was found at index 0 of the filename, substring(0, index - 1) threw a StringIndexOutOfBoundsException (e.g. setFrom("1.0"), mapFileName("1.0.jar")).
2. indexOf matched the first occurrence of the version string, so a version appearing inside the artifactId was stripped instead of the trailing version segment (e.g. a-1.0-b-1.0.jar mapped to a-b-1.0.jar instead of a-1.0-b.jar). A version-like substring not at a segment boundary was also stripped (e.g. a-1.0b.jar → ab.jar).

The mapper now anchors the match to a trailing -<version> segment: it searches for -<version> from the end of the filename and only strips when the version is followed by the file extension (.), a -<classifier> segment, or nothing. Because the match always includes the leading -, the index-0 crash is impossible and the version is no longer stripped from the middle of the artifact id.

Changes

• VersionMapper.java: replace the unanchored indexOf + substring(0, index - 1) with a lastIndexOf('-' + version) loop that validates the trailing segment boundary.
• New unit test VersionMapperTest covering the basic case, classifier handling, the index-0 crash, the wrong-occurrence stripping, the non-boundary substring, directory preservation, and the no-match case.

Verification

• The new tests fail on master (StringIndexOutOfBoundsException and wrong stripped filenames) and pass with the fix.
• mvn verify (rat, checkstyle, spotless, unit tests, javadoc) passes.
• mvn verify -Prun-its passes: all 29 integration tests succeed.