test: migrate math/base/special/beta to ULP-based testing

[ujjwalv01]

Resolves a part of #11352.

Description

What is the purpose of this pull request?

This pull request:

• migrates the tests for math/base/special/beta from computed relative tolerance (EPS-scaled delta <= tol) and absolute tolerance checks to ULP-based assertions;
• replaces the @stdlib/math/base/special/abs require with @stdlib/assert/is-almost-same-value, and corrects the invalid @stdlib/assert/is-nan require path to @stdlib/math/base/assert/is-nan. (The EPS constant is removed as it is no longer required);
• both test/test.js and test/test.native.js are modified to use the new ULP assertions.

ULP bounds (one per fixture set, each tightened to the measured minimum):

fixture set	previous tolerance	ULP bound
R	8e-15 (absolute)	1523
Boost	160.0 * EPS	267

Each bound is the smallest non-negative integer for which every fixture in the corresponding set passes. Starting from a high bound and lowering, the suite passes at the values above, and decrementing each bound by one produces exactly one failure per set, confirming that no bound can be tightened further.

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

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• Code generation (e.g., when writing an implementation or fixing a bug)
• Test/benchmark generation
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Disclosure

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Coverage Report

Package	Statements	Branches	Functions	Lines
math/base/special/beta	$\\color{red}326/339$ $\\color{green}+96.17\\%$	$\\color{red}28/35$ $\\color{green}+80.00\\%$	$\\color{green}3/3$ $\\color{green}+100.00\\%$	$\\color{red}326/339$ $\\color{green}+96.17\\%$

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