feat(nanvmr): add nan-safe vmr accumulator

[AyushiJain18270]

Resolves #{{5627}}.

Description

What is the purpose of this pull request?

This pull request:

• Adds a new incremental variance-to-mean ratio (VMR) accumulator, incr-nanvmr, which safely ignores NaN values.
• Implements and verifies tests, examples, benchmarks, for the accumulator.
• Ensures the accumulator returns null until at least one valid datum is provided and behaves correctly with incremental updates.

Related Issues

Does this pull request have any related issues?

This pull request has the following related issues:

• #{{5627}}

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.".

not applicable .

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@stdlib-js/reviewers

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
stats/incr/nanvmr	$\color{green}133/133$ $\color{green}+0.00%$	$\color{green}10/10$ $\color{green}+0.00%$	$\color{green}2/2$ $\color{green}+0.00%$	$\color{green}133/133$ $\color{green}+0.00%$

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

[Planeshifter]

Flagged some copy & paste errors. Thanks for opening a PR!