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.

include/user/stimulusBuffer.h

@@ -44,6 +44,7 @@ public:
 		inputEngineConstraints,
 		outputEngineConstraints,
 		static_cast<size_t>(histbuffMs / CONFIG_STIMBUFF_FRAME_PERIOD_MS)),
+	stagingBufferPinner(stagingBuffer.makeMlockPinner()),
 	ringBuffer(
 		static_cast<std::shared_ptr<FrameAssemblyDesc>>(stagingBuffer),
 		callbacks, flags)
@@ -51,17 +52,18 @@ public:
 
 	virtual ~StimulusBuffer() = default;
 
-	// Non-copyable, movable
+	// Non-copyable, non-movable: pinner lifetime is tied to this instance
 	StimulusBuffer(const StimulusBuffer&) = delete;
 	StimulusBuffer& operator=(const StimulusBuffer&) = delete;
-	StimulusBuffer(StimulusBuffer&&) = default;
-	StimulusBuffer& operator=(StimulusBuffer&&) = default;
+	StimulusBuffer(StimulusBuffer&&) = delete;
+	StimulusBuffer& operator=(StimulusBuffer&&) = delete;
 
 public:
 	StimulusProducer& parent;
 	std::shared_ptr<device::DeviceAttachmentSpec> deviceAttachmentSpec;
 	int histbuffMs;
 	StagingBuffer stagingBuffer;
+	std::unique_ptr<StagingBuffer::MlockPinner> stagingBufferPinner;
 	SpMcRingBuffer ringBuffer;
 };