Parallel replicas: Enhance min_number_of_marks in ParallelReplicasReadingCoordinator

Why it matters

This change enhances reading coordination between parallel replicas by ensuring that the min_number_of_marks parameter, which influences data partitioning granularity, is better respected. This results in more efficient parallel reading and better load distribution across replicas, improving query performance in distributed setups.

How to use it

To use this improvement, enable the experimental Parallel Replicas feature and configure the min_number_of_marks parameter appropriately in your table settings or reading coordinator. No additional user intervention is typically required beyond enabling the feature and tuning the parameter for your workload.