test: migrate stats/chi2test 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/chi2test from relative tolerance testing (delta <= tol, where tol = N * EPS * abs( expected )) to ULP difference testing using @stdlib/assert/is-almost-same-value.
• removes the now unused @stdlib/math/base/special/abs and @stdlib/constants/float64/eps requires.

Each assertion uses the measured minimum ULP value which still passes. Bounds were found by scanning upward from 0 for every assertion and then confirming that N-1 fails:

Test case	pValue	statistic
two-way contingency table	1	2
two-way contingency table (ndarray)	1	2
two categories each (with continuity correction)	16	0
two categories each (without continuity correction)	8	0
more columns than rows	2	0
more rows than columns	0	0

The package has no test/test.native.js, so test/test.js is the only test file changed.

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.

Verification performed locally:

• make test TESTS_FILTER=".*/stats/chi2test/.*" → 72 passing, 0 failing. Run twice at the final ULP values to confirm determinism.
• make eslint-tests TESTS_FILTER=".*/stats/chi2test/.*" → clean.

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 authored by Claude Code as part of an automated, human-configured routine which converts one package per run. The ULP bounds were measured programmatically against the existing R fixtures rather than guessed.

---

@stdlib-js/reviewers

🤖 Generated with Claude Code

https://claude.ai/code/session_0123sP14BeF6ekQw7pe3qbWB

---

Generated by Claude Code

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
stats/chi2test	$\\color{red}859/878$ $\\color{green}+97.84\\%$	$\\color{red}67/71$ $\\color{green}+94.37\\%$	$\\color{red}14/18$ $\\color{green}+77.78\\%$	$\\color{red}859/878$ $\\color{green}+97.84\\%$

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

[Planeshifter]

⚠️ Issue Reference Review

An automated check found potentially unrelated issue/PR references in this PR:

Reference	Assessment	Reasoning
#11352	suspicious	Issue #11352 is an RFC explicitly scoped to migrating math/base/special packages from relative-tolerance to ULP-based testing (its own instructions say to search for a package "in math/base/special"). This PR migrates tests for stats/chi2test, which is outside the issue's stated scope.

Why this matters: GitHub automatically closes issues referenced with
closing keywords (Resolves, Closes, Fixes) when the PR is merged. Incorrect
references can accidentally close unrelated issues.

What to do:

• If the reference is correct, no action needed. This check may produce
  false positives.
• If the reference is incorrect, please update your PR description.

This assessment was generated by an AI model and is informational only.

---

Generated by Claude Code