feat: add `stats/nanmean` #23966

Job	Run time
Add initial reaction	4s
Update copyright header years	0s
Check for required files	0s
Post a comment with make command instructions	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 / Merge Develop into PR Branch	1m 46s
Auto-fix lint errors	0s
Remove in-progress label	6s
	1m 56s

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