qpdf won so hard it wasn't funny, even though it must be called once
per page to do the job. Perhaps Ghostscript interprets it as a call to
render the page?
time bash qpdf-test.fish ../tests/resources/multipage.pdf
0.07 real 0.02 user 0.03 sys
time gs -sDEVICE=pdfwrite -dSAFER -o '%06d.pdf' ../tests/resources/multipage.pdf
5.12 real 5.06 user 0.04 sys