Updates cross-language-testing

[leerho]

Build/CI

• GitHub Actions bumped (checkout v5→v7, setup-java v5→v6, codeql-action v3→v4)
• serde-compat.yml now manual-trigger only (no more auto push/PR trigger), because DS-TCK is out-of-date.
• pom.xml: TestNG group properties renamed hyphen→underscore to match UtilityIO constants; added a check_rust_files profile and testng.all_groups aggregate; Javadoc doclint tightened none→all, plus a new internal-javadoc-lint pass (explains most of the src/main doc fixes below)

Cross-language test infrastructure

• TestUtil.java/TestUtilTest.java deleted, replaced by new UtilityIO.java/UtilityIOTest.java — paths now resolve lazily via system properties with an IDE/local-run fallback, plus a new GroupLanguage enum (JAVA/CPP/GO/RUST) used to parameterize per-sketch checks
• testng.xml collapsed from 5 hand-maintained blocks down to one, with group filtering now done entirely through Surefire in pom.xml

Per-sketch cross-language tests

Mostly mechanical migration to the new UtilityIO/GroupLanguage pattern, but two are real content changes, not just refactors:

• ReservoirCrossLanguageTest (the 571-line diff) — previously only generated Java files with zero cross-language verification; this branch adds ~24 new check methods giving Reservoir sketches C++/Go/Java cross-checking for the first time
• ReqSketchCrossLanguageTest — assertEquals(weight, 2 * n + 1) widened to 2L * n + 1L, a real int-overflow fix

Main source changes

Nearly all Javadoc cleanup driven by the stricter doclint. One real bug fix buried in there:

• CompactQuantilesDoublesSketch.isReadOnly() now correctly returns true instead of false — a compact (inherently immutable) sketch was misreporting itself as writable

BoundsOnRatios rework

• BoundsOnRatiosInThetaSketchedSets — fixed a backwards javadoc claim; no behavior change otherwise
• BoundsOnRatiosInTupleSketchedSets (157-line diff) — added the missing Theta-vs-Tuple and Theta-vs-Tuple/Theta overloads, completing the 2×2 sketch-type combination matrix; new BoundsOnRatiosInTupleSketchedSetsTest.java covers them

Added Simple output metrics

• Added metrics for files: read, written, and with warnings.
  Because the cross-language testing is becoming so large with multiple languages, these metrics appear at the end of any of the cross-language TestNG group profiles (see end of pom.xml).

Worth flagging

1. Rust support is plumbing-only — CHECK_RUST_FILES, GroupLanguage.RUST, the Maven profile, and getRustPath() all exist, but no test class actually checks a Rust file yet.