docs: improve doctests for complex number instances in math/base/special/csignumf#9042

kgryte merged 2 commits intostdlib-js:developstdlib-js/stdlib:developfrom

prajjwalbajpai:doctest-cmplx-csignumfprajjwalbajpai/stdlib:doctest-cmplx-csignumfCopy head branch name to clipboard