Update NR UE threading model

This updates the NR UE threading model by preventing calling threadpool from threadpool and fixes deadlock issues related to processSlotTX. By making processSlotTX run to completion instead of starting and waiting for other threads to finish it prevents locking thread pool cores, therefore prevening deadlocks.

There is a slight difference here compared to the previous version where I do not use the UL actor as I believe it is not necessary, processSlotTX satisfies the run-to-completion requirement now. If in the future any UL procedure would be parallelized using the thread pool it should either be done in a run-to-completion model or the processSlotTX function should be taken off the thread pool.

Here is the updated model: