feat(matchers): add PQ-gram matcher

[jrfaller]

Summary

• add the registered gumtree-pq matcher, combining subtree-hash anchors with PQ-gram-aware bottom-up candidate scoring
• resolve competing candidates globally in iterative rounds
• allow the Defects4J benchmark task to accept matcher classes with -Pmatchers

Benchmark

Defects4J (1,046 file pairs): gumtree-pq produces 8,827 simplified edit actions versus 9,057 for gumtree-simple (-230; 67 wins, 951 ties, 28 losses).

Validation

• ./gradlew :core:test --tests com.github.gumtreediff.test.TestGumtreeMatcher
• ./gradlew :benchmark:runOnDefects4J ...