refactor: update stats/base/sdsnanmean native addon from C++ to C

[vivekmaurya001]

Resolves None.

Description

• adds C addons to stats/base/sdsnanmean instead of c++ addons

Checklist

Please ensure the following tasks are completed before submitting this pull request.

• Read, understood, and followed the contributing guidelines

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@stdlib-js/reviewers

[vivekmaurya001]

/stdlib update-copyright-years

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
stats/base/sdsnanmean	$\color{green}359/359$ $\color{green}+100.00\%$	$\color{green}14/14$ $\color{green}+100.00\%$	$\color{green}4/4$ $\color{green}+100.00\%$	$\color{green}359/359$ $\color{green}+100.00\%$

The above coverage report was generated for the changes in this PR.

[kgryte]

LGTM