feat: add C `ndarray` interface and refactor implementation for `stats/base/dsnanmeanpn`#4405

kgryte merged 20 commits intostdlib-js:developstdlib-js/stdlib:developfrom

Neerajpathak07:ndarray-dsnanmeanpnNeerajpathak07/stdlib:ndarray-dsnanmeanpnCopy head branch name to clipboard