Samsung made big strides with last year’s foldables in terms of durability — the Z Flip 3 and Z Fold 3 were the first devices in the series to offer serious water resistance and an IPX8 rating. This year’s phones aren’t a whole lot tougher, but the Z Fold 4 and Z Flip 4 are still something of an engineering marvel. We got a glimpse at the foldable assembly line last year, and as the newest Flip and Fold go on sale today, Samsung is giving us another peek at how the sausage is…