feat: add `stats/nanmean` #23975

Job	Run time
Update copyright header years	0s
Add initial reaction	0s
Auto-fix lint errors	0s
Post a comment with make command instructions	0s
Check for required files	0s
Rebase this PR on top of develop branch	0s
Print a list of available slash commands	0s
Merge changes from develop branch into this PR	0s
Remove in-progress label	-1s
	-1s

Provide feedback