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

[Planeshifter]

Resolves a part of #11352.

Description

What is the purpose of this pull request?

This pull request:

• migrates test/test.native.js for math/base/special/pow from relative-tolerance (EPS-based) assertions to ULP-difference assertions via @stdlib/assert/is-almost-same-value, using the minimum required ULP values (verified by direct ULP-difference computation over the test fixtures).
• leaves test/test.js unchanged, as the JavaScript test file contains no relative-tolerance assertions: every fixture block already asserts exact equality via t.strictEqual, and a direct ULP-difference computation over all seven fixture sets confirms a maximum ULP difference of 0 for the JavaScript implementation.
• collapses the obsolete exact-equality short-circuit branches (if ( actual === expected[i] ) { ... } else { ...tolerance... }) in the native test file into single isAlmostSameValue assertions, as isAlmostSameValue covers exact equality.
• uses a maximum ULP difference of 1 for all seven migrated native test blocks, which is larger than the JavaScript counterpart (exact, 0 ULP) due to compiler optimizations which may result in result divergence; accordingly, the canonical NOTE comment (see feat: add C implementation for math/base/special/spence #2298 and commit 69e1068) is added above each migrated assertion.
• preserves the special-case handling for the 5.0e-324 (smallest subnormal) underflow branch in the small x, large y test block.
• retains the EPS and abs requires, as both are still used elsewhere in the native test file.

ULP minimality was verified by confirming that a maximum ULP difference of 0 produces native test failures, while 1 passes all assertions (73605+ assertions across all test files via make test).

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.

The native ULP values were measured on darwin arm64 (clang). CI should confirm the tolerances hold across other platforms and compilers.

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 primarily by Claude Code, including the test migration and the minimum-ULP computation; an independent automated verification pass recomputed the ULP values against the fixtures before opening this PR.

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[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
math/base/special/pow	$\\color{red}1380/1382$ $\\color{green}+99.86\\%$	$\\color{red}118/119$ $\\color{green}+99.16\\%$	$\\color{green}11/11$ $\\color{green}+100.00\\%$	$\\color{red}1380/1382$ $\\color{green}+99.86\\%$

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