test: migrate math/base/special/cospi to ULP-based assertions

[Planeshifter]

Resolves a part of #11352.

Description

What is the purpose of this pull request?

This pull request:

• Migrates the math/base/special/cospi package tests from relative-tolerance (delta/tol/EPS) comparisons to ULP-based assertions using @stdlib/assert/is-almost-same-value, per the tracking issue.
• Updates both test/test.js and test/test.native.js, each of which had a single fixture-driven test block ('the function computes cos(πx)') using the old idiom.
• The minimum ULP tolerance was determined empirically: 1 passes reliably for both the JS and native implementations, while 0 (exact equality) fails (380 of 6214 cases). The test suite was run twice at ULP 1 for both files to confirm deterministic results.
• No other test cases were touched; only the tolerance-based comparisons were converted.

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.

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 authored by Claude Code, run as an unattended scheduled task. It searched the repository for a package still using the old relative-tolerance test idiom, cross-checked existing open/merged ULP-migration PRs to avoid duplicating work, studied prior-art commits (e.g. the atan2d, powm1, and cceiln conversions) to mirror the established idiom, converted the tolerance checks to isAlmostSameValue, and empirically determined the minimum passing ULP bound by testing both 1 and 0 and confirming determinism across repeated runs.

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@stdlib-js/reviewers

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Generated by Claude Code

[stdlib-bot]

Hello! 👋

We've noticed that you've been opening a number of PRs addressing good first issues. Thank you for your interest and enthusiasm!

Now that you've made a few contributions, we suggest no longer working on good first issues. Instead, we encourage you to prioritize cleaning up any PRs which have yet to be merged and then proceed to work on more involved tasks.

Not only does this ensure that other new contributors can work on things and get ramped up on all things stdlib, it also ensures that you can spend your time on more challenging problems. 🚀

For ideas for future PRs, feel free to search the codebase for TODOs and FIXMEs and be sure to check out other open issues on the issue tracker. Cheers!

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
math/base/special/cospi	$\\color{green}217/217$ $\\color{green}+100.00\\%$	$\\color{green}20/20$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}217/217$ $\\color{green}+100.00\\%$

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