feat: add stats/incr/nanvmr

[anxhukumar]

Resolves #5627

Description

What is the purpose of this pull request?

This pull request:

• Adds the @stdlib/stats/incr/nanvmr package, which incrementally computes variance-to-mean ratio while ignoring NaN values.

Related Issues

Does this pull request have any related issues?

This pull request:

• resolves [RFC]: add stats/incr/nanvmr #5627

Questions

Any questions for reviewers of this pull request?

No.

Other

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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-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
stats/incr/nanvmr	$\color{green}133/133$ $\color{green}+100.00\%$	$\color{green}9/9$ $\color{green}+100.00\%$	$\color{green}2/2$ $\color{green}+100.00\%$	$\color{green}133/133$ $\color{green}+100.00\%$

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