test: migrate stats/incr/nanskewness to ULP-based assertions

[kgryte]

Resolves a part of #11352.

Description

What is the purpose of this pull request?

This pull request:

• Migrates the tests for stats/incr/nanskewness from relative-tolerance testing to ULP (units in the last place) difference testing, per the tracking issue.
• Replaces both delta/tol (EPS-based) comparisons in test/test.js with @stdlib/assert/is-almost-same-value. The package has no test/test.native.js, so test/test.js is the only changed file.
• The minimum required ULP bound was determined by computing the actual ULP difference between observed and expected values for every non-null expected value in both test cases. The maximum observed difference was 1 ULP, so both assertions use isAlmostSameValue( actual, expected, 1 ).
• Minimality was verified by re-running the suite at 0 ULPs, which fails 6 assertions; 1 is therefore the tightest bound which passes.
• The test suite was run twice at this bound to confirm deterministic results (no FMA/architecture-related flakiness).
• The existing expected[ i ] === null branch in the accumulator loop is retained as-is, since it asserts the accumulator's null return prior to three data points and is not part of the tolerance idiom being migrated.

Related Issues

Does this pull request have any related issues?

This pull request has the following related issues:

• [RFC]: Migrate math/base/special packages from relative tolerance testing to ULP difference testing (tracking issue) #11352

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.

make lint-javascript-tests is clean for the changed file. The editorconfig-checker step could not be executed in the authoring environment, as the package downloads its binary from a GitHub release which was unreachable; the file was instead checked manually against .editorconfig (tab indentation, LF line endings, UTF-8, no trailing whitespace, final newline).

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.".

This PR was written by Claude Code, following the conventions established in already-merged ULP migration PRs (e.g. #14255, #14252, #14163). The minimum ULP bound was determined empirically by computing actual ULP differences, not guessed.

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@stdlib-js/reviewers

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Generated by Claude Code

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
stats/incr/nanskewness	$\\color{green}134/134$ $\\color{green}+100.00\\%$	$\\color{green}7/7$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}134/134$ $\\color{green}+100.00\\%$

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