Batch optimized SparkRunner groupByKey

[twosom]

Please add a meaningful description for your change here

fixes #20943

This PR improves the performance of GroupByKey transform in SparkRunner by replacing the current implementation that uses Spark's groupByKey with combineByKey.

The current implementation uses Spark's groupByKey which causes all the data to be shuffled across the network before grouping. This can lead to significant performance overhead and potential OOM issues with large datasets.

By switching to Spark's combineByKey, we can:

• Perform partial combining at the map side before shuffling
• Reduce the amount of data transferred across the network
• Improve memory utilization and overall performance

Before optimized - 6.1GiB for shuffle

After optimized - 1487.7MiB for shuffle.

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[twosom]

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[damccorm]

Thanks - had a few questions, but overall it seems like an improvement

[twosom]

@damccorm
Thanks for your question! I've added the explanation as a comment on the PR.

[damccorm]

This LGTM, I'm rerunning the failing test suite to see if we can get a green signal before merging though (failure was due to pulling Java licenses, so likely unrelated to this change)