A Tower Ground Controller reported tower positions were combined due to lack of staffing and no one in the tower noticed the Local Controller taxied an aircraft across a runway at the same time another aircraft was departing.

Narrative

I was on Ground Control during this event; and both aircraft involved were talking to and being controlled by the Local controller. Local1 and Local2 were combined with a stand alone OS/CIC (Operations supervisor / Controller in Charge) as well. Local Control had an aircraft (Aircraft X) landing roll in RWY 12R with a departure (Aircraft Y) on RWY 12L. Local Control told Aircraft X to turn left on Taxiway B and cross RWY12L. I think Local Control forgot about the departure or thought they were already past Taxiway B when he issued the crossing instructions to Aircraft Y. Aircraft Y ended up crossing right in front of Aircraft X as they were departing. I did not see it happen from Ground Control as I had just taxied an unrelated aircraft to this incident and was scanning my taxiways. The standalone OS/CIC also did not observe it. We only realized what happened after Aircraft Y told Local Control that someone crossed in front of them.I think a major contributing factor to this event; is our Air Traffic Manager (ATM) and people above our ATM are making a major push to have a standalone OS/CIC to the max extent possible. Due to this; there are times when we combined ALL positions (I.e GC/CD/FD/LC1/LC2) to one person just to have a standalone CIC. Our facility has also been severely understaffed recently. This is the worse I've seen our staffing in the many years I have been here. We are going to lose even more people in the next 6-9 months with no replacements in sight. In this case; we had locals combined to make it so we could have a standalone CIC. Prioritizing having a standalone CIC was a major contributing factor to this incident happening. We could have had the tower configured to make me be on LC2; the other controller be on LC1; and have the supervisor be combined with GC/CIC. If that was the tower configuration; this event would not have happened. LC1 would not have lost track of his RWY 12L departure while trying to taxi his RWY 12R arrival across 12L. The LC (Local Control) would have had less runways and less aircraft to worry about had the locals been split. OS/CIC; especially the one that was up in the tower at the time; rarely ever catches anything before it happens anyways.In most situations; it is MUCH safer to have the control position split off even if that means having CIC combined with GC. This makes it so the controller has less airspace; less runways; and less aircraft to keep track of. While our staffing is low; our ATM and people higher up in the FAA need to be ok combining CIC with GC if that means having all the position split off especially during moderate+ traffic. If this does not change; eventually a controller that is over saturated from working too many positions is going to make another mistake the CIC won't catch and someone will die just so we could have a standalone CIC. Once we get our staffing back up; or on days when our staffing is good; sure lets have a standalone CIC. We are sacrificing safety just for the sake of having a standalone CIC who never catches any mistakes anyways.