feat: add C ndarray interface and refactor implementation for stats/base/dnanmean

[Neerajpathak07]

Resolves none

Description

What is the purpose of this pull request?

This pull request:

• adds C ndarray interface for stats/base/dnanmean
• refactor JavaScript implementation
• refactor examples, tests, docs and benchmarks in manifest.json

Related Issues

Does this pull request have any related issues?

This pull request:

• resolves #{{TODO: add issue number}}

Questions

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No.

Other

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No.

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

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
stats/base/dnanmean	$\color{green}345/345$ $\color{green}+100.00\%$	$\color{green}13/13$ $\color{green}+100.00\%$	$\color{green}4/4$ $\color{green}+100.00\%$	$\color{green}345/345$ $\color{green}+100.00\%$

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

[Neerajpathak07]

I have made the changes to other PR's as well.

[Neerajpathak07]

/stdlib update-copyright-years

[Neerajpathak07]

@kgryte Pls take a look at this.

[kgryte]

LGTM