StagingBuff: support both Mlock & IOUring pin; Use in IoUAssmEngn

We use io_uring_register_buffers() for IoUringAssemblyEngine instead
of using mlock(). This __appears__ to have reduced CPU utilization on
the Dell laptop. Could also be that we recently upgraded total RAM
from 8GiB to 32GiB.

stimBuffApis/livoxGen1/pcloudStimulusProducer.cpp

@@ -95,10 +95,13 @@ collationBuffer(
 	StagingBuffer::IOEngineConstraints::openClInputConstraints,
 	StagingBuffer::IOEngineConstraints::openClInputConstraints,
 	nDgramsPerStagingBufferFrame),
+collationBufferMlockPinner(collationBuffer.makeMlockPinner()),
 averageIntensityBuffer(
 	openClAverageIntensityConstraints,
 	openClAverageIntensityConstraints,
 	nDgramsPerStagingBufferFrame),
+averageIntensityBufferMlockPinner(
+	averageIntensityBuffer.makeMlockPinner()),
 tempStimulusFrameMem(0),
 tempStimulusFrame(
 	FrameAssemblyDesc::SlotDesc{