feat: add stats/incr/nanmsumabs2

[abdoo303]

Resolves #5612.

Description

What is the purpose of this pull request?

This pull request:

• add stats/incr/nanmsumabs2, an accumulator for incrementally computing a moving sum of squared absolute values, ignoring NaN values

Related Issues

Does this pull request have any related issues?

This pull request has the following related issues:

• [RFC]: add stats/incr/nanmsumabs2 #5612

Questions

Any questions for reviewers of this pull request?

No.

Other

Any other information relevant to this pull request? This may include screenshots, references, and/or implementation notes.

This implementation makes use of the existing @stdlib/stats/incr/msumabs2 package (which does not handle NaN values) and adds a NaN-skipping guard around it, following the same pattern used by @stdlib/stats/incr/nanmsumabs, which uses @stdlib/stats/incr/msumabs in the same way.

Checklist

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

• Read, understood, and followed the contributing guidelines.

AI Assistance

When authoring the changes proposed in this PR, did you use any kind of AI assistance?

• Yes
• No

If you answered "yes" above, how did you use AI assistance?

• Code generation (e.g., when writing an implementation or fixing a bug)
• Test/benchmark generation
• Documentation (including examples)
• Research and understanding

Disclosure

If you answered "yes" to using AI assistance, please provide a short disclosure indicating how you used AI assistance. This helps reviewers determine how much scrutiny to apply when reviewing your contribution. Example disclosures: "This PR was written primarily by Claude Code." or "I consulted ChatGPT to understand the codebase, but the proposed changes were fully authored manually by myself.".

I used Claude Code in order follow the conventions and better comprehend similar existing work in stats/incr/msumabs2 and stats/incr/nanmsumabs packages.

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[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
stats/incr/nanmsumabs2	$\\color{green}142/142$ $\\color{green}+100.00\\%$	$\\color{green}7/7$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}142/142$ $\\color{green}+100.00\\%$

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