Refactor PHPUnit support into separate phpunit-junit parser
Instead of modifying the Java JUnit parser, this creates a dedicated
PHPUnit parser that properly handles PHPUnit's nested testsuite elements.
This keeps the parsers cleanly separated and allows for future PHPUnit-
specific features.
Co-Authored-By: Matteo Beccati <matteo@beccati.com>
Co-Authored-By: Claude Code <noreply@anthropic.com>
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