simulate: course_flow counts batch wait inside WIP and reports it (flow model B6) #5545

course_flow releases WIP before the daily batch, so the daily-batch wait sits outside the WIP cap and is not reported. Add an opt-in WIP cap that counts the batch wait, and report the mean batch wait. Little's law must hold within 0.5% with the batch wait inside WIP. The daily batch itself stays.

keep-open: nothing fixes it yet