feat: add C implementation for stats/base/ndarray/dnanmeanpn

[ujjwalv01]

Resolves a part of #14034

Description

What is the purpose of this pull request?

This pull request:

• Adds a native C implementation for @stdlib/stats/base/ndarray/dnanmeanpn
• Includes corresponding C and JavaScript benchmark suites
• Exposes native bindings via Node-API
• Adds tests to ensure parity between JavaScript and C implementations

Related Issues

Does this pull request have any related issues?

This pull request has the following related issues:

• [RFC] : add C implementations for @stdlib/stats/base/ndarray packages (tracking issue) #14034

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.

No.

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 utilized AI assistance strictly to help check, split, and reformat the existing JavaScript test and benchmark suites for the native implementation fallback logic. The C implementation and native architecture were manually verified.

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@stdlib-js/reviewers

[stdlib-bot]

Coverage Report

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[kgryte]

LGTM after clean-up.