image_range is not a range

[rbrugo]

The following code does not compile:

auto img = spl::graphics::image{...};
std::ranges::for_each(img.rows(), [](auto){}); // fails
std::for_each(img.rows().begin(), img.rows.end(), [](auto){}); // fails - no operator *
for (auto && row : img.rows()) { } // fails - no operator *