fre.cmor: replace nccmp subprocess calls with netCDF4 in cmor run subtool tests#826

Copilot wants to merge 4 commits intomainNOAA-GFDL/fre-cli:mainfrom

copilot/remove-replace-nccmp-from-testsNOAA-GFDL/fre-cli:copilot/remove-replace-nccmp-from-testsCopy head branch name to clipboard