The application of ds() and assemble() to calculate the drag and lift coefficients of the flow around a cylinder

Hi, Dr. Dokken! I am having another issue with my code. Initially I accidentally integrated over the whole domain and get some values of the drag and lift coefficients, but I later found out that when I integrate near the boundary of the cylingder, the drag and lift coefficients are always 0 no matter the timestep.
My code now can be found here: Getting 0 drag coefficient and lift coefficient when working on the flow over a cylinder - General - FEniCS Project.

I would be more than grateful if you could help me again!!