feat: add incrnanmmeanvar (moving mean/variance with NaN skipping) (fixes #5592)

[anoofmhd]

Resolves #5592.

Description

What is the purpose of this pull request?

This pull request:

• Adds a new incremental moving mean and variance accumulator: @stdlib/stats/incr/nanmmeanvar.

• This module behaves similarly to @stdlib/stats/incr/mmeanvar, but skips NaN values instead of propagating them.

• Includes implementation, tests, documentation, TypeScript definitions, REPL help file, benchmarks, and examples.

Related Issues

Does this pull request have any related issues?

This pull request has the following related issues:

• [RFC]: add stats/incr/nanmmeanvar #5592

Questions

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No.

Other

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• Read, understood, and followed the contributing guidelines.

AI Assistance

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I used ChatGPT to assist in understanding spec expectations and drafting documentation wording.
The implementation and test logic were written and verified manually.

---

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Coverage Report

Package	Statements	Branches	Functions	Lines
stats/incr/nanmmeanvar	$\color{green}138/138$ $color{green}+100.00%$	$\color{green}11/11$ $color{green}+100.00%$	$\color{green}2/2$ $color{green}+100.00%$	$\color{green}138/138$ $color{green}+100.00%$

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

[kgryte]

/stdlib update-copyright-years

[kgryte]

Suggested change

	module.exports = incrnanmmeanvar;
	module.exports = incrnanmmeanvar;

This file is missing a trailing newline.