feat: support PHPUnit 13

[jdreesen]

Based on #56 (PHPUnit 12 support), so this PR targets that branch. Retarget to main once #56 is merged.

Summary

• Allow phpunit/phpunit ^13.4 (PHP >= 8.4.1 only) and extend the CI matrix: PHP 8.1-8.3 are excluded, plus one lowest-dependency run (Pimcore 2026 / PHP 8.4); --fail-on-risky now applies to the newest PHPUnit.
• PHPUnit 13 replaced the private TestCase::$data array with a DataSet value object. AttributeProvider writes the data with the configuration objects stripped back via reflection, which no longer worked. That part now goes through a new setProvidedData() that picks the property for the installed PHPUnit version (same style as the existing getTestName()/getProvidedData() switches).
• PHPStan baseline and composer-dependency-analyser.php ignore the DataSet class on versions that don't have it (reportUnmatched: false / conditional ignore, so both sides stay clean).
• Everything else removed in PHPUnit 13 isn't used here. DAMA's extension only uses event classes that still exist.
• README: the "Data Provider" note now recommends only the positional #[DataProvider('...', false)]. PHPUnit marks its attributes @no-named-arguments, so the named validateArgumentCount: false isn't covered by its BC promise (and fails on PHPUnit 10/11). The <details> section for multi-version projects is gone since the positional form works everywhere.
• CHANGELOG (v0.15.1), CLAUDE.md and test comments updated.

Test plan

• Full suite locally with PHPUnit 13.4.1 / PHP 8.5.9 / --fail-on-risky: 109 tests, 0 failures, 0 warnings
• Full suite locally with PHPUnit 12.5.38 (other side of the version switch): same result
• PHPStan (phpstan-2026.neon) and composer-dependency-analyser clean on PHPUnit 13 and 12
• CI matrix incl. the new PHPUnit 13 jobs and the PHPUnit 9/10/11/12 jobs (all 43 checks green; the changed AttributeProvider code runs on all of them)

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