Wrong log timestamp for reconstruction

When using CudaFullFieldPipeline[LimitedMemory], the time difference between "Start reconstruction" and "End Reconstruction" is almost zero. It is due to the fact that the _reconstruct() method just enqueues many asynchronous 2D FBP and returns "immediately".

The step coming right after (histogram or get data from GPU) is therefore perceived as "slow", as its timestamp includes the actual reconstruction time.