Bugfix,IoUringEngn: fill unassembled slots w/dummy; use separate iovecs

We implemented the feature to fill unassembled slots w/dummy header
values for the livox pcloud header.

We also fixed a bug where io uring was writing into the last slot
only because we were using the same iovec for every SQE.

stimBuffApis/livoxGen1/ioUringAssemblyEngine.h

@@ -28,7 +28,8 @@ class PcloudStimulusBuffer;
 class IoUringAssemblyEngine
 {
 public:
-	explicit IoUringAssemblyEngine(PcloudStimulusBuffer& parent);
+	explicit IoUringAssemblyEngine(
+		PcloudStimulusBuffer& parent, size_t nDgramsPerStagingBufferFrame);
 	~IoUringAssemblyEngine() = default;
 
 	bool setup();
@@ -72,7 +73,21 @@ private:
 	SpinLock isAssemblingLock;
 	bool isAssembling;
 
-	void cancelIncompleteAndFillDummies();
+	// Number of datagrams per staging buffer frame
+	size_t nDgramsPerStagingBufferFrame;
+
+	struct SlotAssemblyDesc
+	{
+		bool assembled;
+		struct msghdr msgHdr;
+		struct iovec ioVec;
+	};
+
+	// Track which slots have been successfully assembled and maintain persistent iovecs
+	std::vector<SlotAssemblyDesc> assembledSlotsTracker;
+
+	void fillUnAssembledSlotsWithDummyDgrams();
+	void printSlotBytes(size_t slotIndex, size_t nBytes);
 	void onEventfdRead(
 		const boost::system::error_code& error, std::size_t bytes_transferred);