round robin load balance

[thorstenhater]

The current partition load balance gets a sibling: round-robin load balance.
This is helpful when consecutive ranges contain similar cells, but the overall
balance is off.

When trying out the Allen V1 model on JUWELS, we get this using partition

---- meters -------------------------------------------------------------------------------
meter                         time(s)      memory(MB)
-------------------------------------------------------------------------------------------
model-init                  10912.980        1679.208
model-run                     995.572        5718.083
meter-total                 11908.552        7397.291

and this using round-robin

---- meters -------------------------------------------------------------------------------
meter                         time(s)      memory(MB)
-------------------------------------------------------------------------------------------
model-init                   4782.748        1535.923
model-run                     496.480        6460.236
meter-total                  5279.228        7996.159