IoUringAssmEngn: add assembleFrameReq

Invoke it instimFrameProductionTimesliceInd.

Also, we discovered:
* stream_descriptor::release() doesn't fully release all metadata
  from the fd it was assigned. This suggests that we should go
  through the codebase and do: release()=>reset() whenever we
  wish to release().
* We've confirmed that spinlocks can be used to prevent race
  conditions between stop() and handler methods.

stimBuffApis/livoxGen1/pcloudStimulusBuffer.cpp

@@ -68,6 +68,16 @@ void PcloudStimulusBuffer::stop()
 
 void PcloudStimulusBuffer::stimFrameProductionTimesliceInd()
 {
+	ioUringAssemblyEngine.assembleFrameReq(
+		{nullptr, [this](bool success, AsynchronousLoop loop) {
+			if (!success) {
+				std::cerr << __func__ << ": Failed to assemble frame" << std::endl;
+			} else {
+				std::cout << __func__ << ": Successfully assembled frame "
+					<< loop.nSucceeded.load() << " slots succeeded "
+					<< "out of " << loop.nTotal << " total slots" << std::endl;
+			}
+		}});
 	// Release the spinlock for now
 	frameAssemblyRateLimiter.release();
 }