test: migrate stats/base/dists/normal/mean to ULP-based assertions

[kgryte]

Resolves a part of #11352.

Description

What is the purpose of this pull request?

This pull request:

• migrates the tests for @stdlib/stats/base/dists/normal/mean from relative-tolerance assertions to ULP-based assertions using @stdlib/assert/is-almost-same-value, per the guidance in [RFC]: Migrate math/base/special packages from relative tolerance testing to ULP difference testing (tracking issue) #11352.
• updates both test/test.js and test/test.native.js to mirror the idiom used in previously converted packages (e.g. stats/base/dists/frechet/variance, stats/base/dists/chi/stdev, stats/base/dists/weibull/stdev), retaining the existing expected[i] !== null fixture guard.
• replaces the previous 1.0 * EPS * abs( expected[ i ] ) tolerance loops in both files with t.strictEqual( isAlmostSameValue( y, expected[ i ], 0 ), true, 'returns expected value' ).
• drops the now-unused @stdlib/math/base/special/abs and @stdlib/constants/float64/eps requires.

The tightest ULP bound was determined empirically by measuring the maximum ULP difference over the full 100-value Julia fixture set:

• test/test.js: N = 0 ULP. Every fixture value matches the Julia reference bit-for-bit, so the measured maximum ULP difference is 0, and 0 is the tightest bound expressible.
• test/test.native.js: N = 0 ULP. The native add-on was built locally for this package so that the native tests were exercised rather than skipped, and the maximum ULP difference for the C implementation over the same fixtures is likewise 0.

This is expected: both implementations return mu verbatim once the NaN/nonpositive-sigma guards are cleared, so no rounding is introduced and the previous tolerance branch was never taken.

Both test/test.js and test/test.native.js were run twice at the final N = 0 (110 assertions each, all passing, with the native add-on built) to confirm the bound is deterministic. Linting via make lint-javascript-tests TESTS_FILTER=".*/stats/base/dists/normal/mean/.*" is clean, and only the two test files are changed.

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

This PR was authored by Claude Code (Anthropic) running as an unattended scheduled task. The conversion mirrors the exact idiom used in previously merged ULP migrations authored by the PR author (e.g. #14434, #14447, #14469), and the ULP bound was measured empirically against the existing Julia fixtures for both the JavaScript and the locally built C implementation.

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@stdlib-js/reviewers

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Generated by Claude Code

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
stats/base/dists/normal/mean	$\\color{green}175/175$ $\\color{green}+100.00\\%$	$\\color{green}9/9$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}175/175$ $\\color{green}+100.00\\%$

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