[Feat][Spark] Efficiency tuning for GraphAr spark

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- [ ] convert sequence process to parallel #328

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Review issue #328 first, then locate the GraphAr Spark sequence-processing path related to the requested parallel conversion. Clarify the intended efficiency goal and success criteria before changing the processing approach; the issue currently does not name files, tests, or a measurable definition of done.

Written by the indexing model from the issue text.