Add Spark example using ask-and-tell interface

spark/ask_and_tell_spark.py

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+"""
+Spark with Ask-and-Tell
+
+An example showing how to use Optuna's ask-and-tell interface with Apache Spark
+to distribute the evaluation of trials.
+
+This script uses PySpark's RDD to parallelize a simple quadratic function.
+"""
+
+import optuna
+from pyspark.sql import SparkSession
+
+
+def evaluate(x):
+    return (x - 2) ** 2  # Simulate a trial evaluation on a Spark worker node
+
+
+if __name__ == "__main__":
+    spark = SparkSession.builder.appName("OptunaSparkExample").getOrCreate()
+    study = optuna.create_study()
+
+    for i in range(20):
+        trial = study.ask()
+        x = trial.suggest_float("x", -10, 10)
+        rdd = spark.sparkContext.parallelize([x])
+        result = rdd.map(evaluate).collect()[0]
+        study.tell(trial, result)
+        print(f"Trial#{trial.number}: {x=:.4e}, {result=:.4e}")
+
+        print("\nBest trial:")
+        print(f"\tValue: {study.best_value}")
+        print(f"\tParams: {study.best_trial.params}")
+        spark.stop()

spark/requirements.txt

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+optuna
+pyspark  # used for SparkSession and RDD parallelism