One Tesla Semi swallows the battery cells of ten Model 3s. That single number explains why a truck unveiled in 2017 only hit volume production today, almost nine years later. The regulatory filing puts the long-range Semi's pack at 822 kWh. A Model 3 carries about 80. So every truck rolling off the new Nevada line eats the cell supply of ten cars. Now run that math backward to 2019, when the Semi was supposed to launch. Tesla couldn't make enough cells for its cars, let alone trucks. Ten…