CASSANDRA-21126: Vector search support in cassandra-easy-stress

[dracarys09]

Summary of the changes

• Add VectorSearch workload for benchmarking Cassandra 5.0+ vector search (ANN) capabilities
• Support both synthetic random vectors and realistic datasets via HDF5 files (SIFT, GloVe, etc.)
• Implement recall@K calculation with ground truth comparison for measuring search quality
• Add configurable similarity functions (COSINE, EUCLIDEAN, DOT_PRODUCT) and vector dimensions

Testing

• Run ./gradlew test --tests "org.apache.cassandra.easystress.workloads.VectorSearchTest"
• Verify workload runs against a Cassandra 5.0+ cluster with random vectors
• Test with an HDF5 dataset (e.g., sift-128-euclidean.hdf5) and verify recall metrics are logged
• Confirm ktlint passes: ./gradlew ktlintCheck

[michaeljmarshall]

This classifies recall as 0 if the relevantTruth.size is 0. I wonder if it makes more sense to exclude this query's recall result from the recall averages and instead track/report the number of queries that didn't have any of the ground truth results inserted into the table?

[dracarys09]

That's a good point. Thanks for the review. I've updated the code to now track such queries separately to keep the recall numbers clean.