test: migrate math/base/special/atan2f to ULP-based assertions

[Planeshifter]

Resolves a part of #11352.

Description

What is the purpose of this pull request?

This pull request:

• Migrates math/base/special/atan2f test cases from relative-tolerance testing to ULP (units in the last place) difference testing, per the guidance in [RFC]: Migrate math/base/special packages from relative tolerance testing to ULP difference testing (tracking issue) #11352.
• Replaces the delta/tol relative-tolerance checks in the three fixture-driven test cases (x and y both positive; x negative, y positive; x and y both negative) in test/test.js and test/test.native.js with t.strictEqual( isAlmostSameValue( actual, expected[ i ], N ), true, 'returns expected value' ), using @stdlib/number/float32/base/assert/is-almost-same-value (matching the convention used by sibling float32 functions such as atanf and hypotf).
• Determines the minimum required ULP tolerance for each fixture group by computing the exact ULP difference between actual and expected values across the full fixture set: positivePositive → 2 ULPs (5001 cases), negativePositive → 1 ULP (1001 cases), negativeNegative → 1 ULP (1001 cases). Both test.js and test.native.js use the same bounds, mirroring the recently converted math/base/special/atan2d (same underlying algorithm, JS vs. native).
• Removes the now-unused absf/EPS imports.

Verified: node test/test.js passes 7062/7062 assertions at the tightened bounds, run twice back-to-back with identical results (no flakiness). npx eslint is clean on both changed files. The native addon is not built in this environment, so test.native.js ULPs were set to match the JS bounds (same as the atan2d precedent) rather than independently measured; test.native.js assertions are skipped (not failed) when the addon is absent.

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?

• Test/benchmark generation

Disclosure

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This PR was authored end-to-end by Claude Code, run as a scheduled/unattended task on my account. It found the candidate package, studied prior art (issue #11352 and the atan2d conversion), applied the ULP migration, computed the tightest ULP bounds directly from the fixtures, and verified tests/lint pass. Opened as a draft so I can review before it goes further.

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@stdlib-js/reviewers

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Generated by Claude Code

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
math/base/special/atan2f	$\\color{green}318/318$ $\\color{green}+100.00\\%$	$\\color{green}26/26$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}318/318$ $\\color{green}+100.00\\%$

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