[Harness] Rewrite benchmark harness in Java with rigorous measurement protocol

[abdessamad-abdoun]

Rewrite the benchmark harness from Groovy to Java 21, with a reproducible measurement protocol (JVM warmup, 3 repetitions, median, memory delta).

Motivation

The current Groovy code has several issues:

Unstable memory measurement (dependent on GC timing)
No repetitions → non-reproducible results
Cumulative measurement across files → cannot isolate the cost of a single file
No JVM warmup → first result biased by JIT compilation
French locale bug on decimal separators in CSV output

Objectives

1. Generic TripleStoreDriver interface

public interface TripleStoreDriver {
    void init();
    void load(String filePath);
    void query(String sparql);
    long getGraphSize();
    void clear();
    void close();
}

2. Measurement protocol

For each file:
  warmup: load() → clear() → gc()    // discarded
  Repeat 3 times:
    gc()
    memory snapshot before
    load()
    memory snapshot after
    gc()
  → median of 3 repetitions
  → memoryDelta = after - before

3. Collected metrics

loadingTimeMs (median over 3 repetitions)
throughputTriplesPerSec
memoryDeltaMb (real delta, not global heap)
cpuPercent (via OperatingSystemMXBean)

4. JSON output format

{
  "metadata": {
    "generatedAt": "...",
    "protocol": { "repetitions": 3, "warmup": true }
  },
  "runs": [
    {
      "engine": "corese.4.6.5",
      "dataset": "dbpedia",
      "file": "category_labels.nt",
      "triples": 565108,
      "loadingTimeMs": 12310,
      "throughputTriplesPerSec": 45890,
      "memoryDeltaMb": 424.8,
      "cpuPercent": 78.2
    }
  ]
}

Files to delete

src/main/groovy/*.groovy
python-utils/plot-compare.py
python-utils/template.html
public/
Files to create

src/main/java/fr/inria/corese/benchmark/driver/TripleStoreDriver.java
src/main/java/fr/inria/corese/benchmark/harness/BenchmarkHarness.java
src/main/java/fr/inria/corese/benchmark/metrics/MetricsCollector.java
src/main/java/fr/inria/corese/benchmark/metrics/BenchmarkResult.java
src/main/java/fr/inria/corese/benchmark/Main.java
Update build.gradle for Java 21, remove Groovy