feat(benchmarks): expand multilingual stemming quality evaluation

* cover all Radixor dictionary languages
* add PRIMARY_OUTPUT, ANY_CANDIDATE, and ALL_CANDIDATES policies
* measure pairwise over-stemming and under-stemming
* add balanced accuracy and complementary quality metrics
* compare single-output and multi-output stemmers fairly
* improve result validation, reporting, and documentation
* move stemming quality tests into the standard test source set
* preserve the existing JMH benchmark structure and badge output

.gitignore

@@ -37,6 +37,7 @@ local.properties
 .settings/
 .loadpath
 .recommenders
+.classpath
 
 # External tool builders
 .externalToolBuilders/