There are no maximum width rules in sky130 but I have never been certain whether they apply slotting during mask generation. They haven't mentioned it. Regardless, I would expect that metal under pad is not subject to slotting, and/or top level metal might not be subject to slotting. That said, however, how do you intend to get metal 4 pads in a 5-metal process? Also---MPW runs through Google cannot allow pads in user projects because they would interfere with the solder bump masks. On ChipIgnite runs slated for QFN packages, you can do pretty much whatever you want.