`PinnedMemoryPool` `initial_size` property was removed due to this [rmm observation ](https://github.com/rapidsai/rmm/issues/1931). But recent benchmarking #781 shows that priming the pinned memory pool is important. [Discussion](https://nvidia.slack.com/archives/C08469RJMRB/p1768347911474639)