test: migrate stats/base/dists/f/kurtosis to ULP-based assertions

[Planeshifter]

Resolves a part of #11352.

Description

What is the purpose of this pull request?

This pull request:

• migrates stats/base/dists/f/kurtosis from relative tolerance testing to ULP difference testing, per the migration described in [RFC]: Migrate math/base/special packages from relative tolerance testing to ULP difference testing (tracking issue) #11352.
• replaces the EPS-scaled delta/tolerance comparison in test/test.js and test/test.native.js with isAlmostSameValue-based assertions.
• final ULP bound: 0 for both test.js and test.native.js. This was found by starting at a generous ULP value and iteratively lowering it until reaching the minimum value at which all fixtures still pass (verified deterministic across repeated runs).

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

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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.".

This PR was written by Claude Code, following the exact idiom established by prior merged conversions in the same stats/base/dists/f/* family (e.g. f/mean, f/skewness, f/stdev). The tests were run locally (including building the native addon) to determine the minimum passing ULP bound.

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🤖 Generated with Claude Code

https://claude.ai/code/session_01N7bMWtHvGQrc61GAtPMjET

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[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
stats/base/dists/f/kurtosis	$\\color{green}210/210$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}210/210$ $\\color{green}+100.00\\%$

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

[stdlib-bot]

Thank you for working on this pull request. However, we cannot accept your contribution as the issue this pull request seeks to resolve has already been addressed in a different pull request or commit.

Thank you again for your interest in stdlib, and we look forward to reviewing your future contributions.