test: migrate constants/float16/ln-half to ULP-based assertions

[kgryte]

Resolves a part of #11352.

Description

What is the purpose of this pull request?

This pull request:

• migrates the test suite of @stdlib/constants/float16/ln-half from relative tolerance testing to ULP difference testing.
• replaces the absf( v - FLOAT16_LN_HALF ) <= EPS tolerance comparison with isAlmostSameValue( v, FLOAT16_LN_HALF, 0 ), using @stdlib/number/float16/base/assert/is-almost-same-value (the half-precision assertion utility, matching the idiom already used by sibling packages such as constants/float16/ln-ten and constants/float16/half-ln-two).
• rounds the computed lnf(0.5) value to half-precision via @stdlib/number/float64/base/to-float16 before comparison, so that the ULP difference is measured in half-precision units.
• removes the now unused @stdlib/math/base/special/absf and @stdlib/constants/float16/eps requires.

Final ULP constant: 0. Starting from a high bound (64) and tightening (64 → 16 → 4 → 1 → 0), the measured maximum ULP difference between float64ToFloat16( lnf( 0.5 ) ) and the exported constant is 0 — both are the bit-identical half-precision value -0.693359375 — so 0 is the minimum required ULP value. The package test suite was run twice at the final bound and passed deterministically both times (4 passing, 0 failing).

Only test/test.js is modified; there is no test/test.native.js for this package.

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.

JavaScript linting of the changed file with etc/eslint/.eslintrc.tests.js is clean. Note that make lint-javascript lints the full src tree and currently reports a pre-existing, unrelated error in etc/typedoc/theme/assets/js/theme.js; that file is untouched by this pull request. The changed file was additionally verified against .editorconfig (LF line endings, UTF-8, tab indentation, no trailing whitespace, final newline).

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
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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, which located the package, mirrored the conversion idiom from already-migrated sibling packages, measured the minimum ULP bound, and ran the tests and linters.

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https://claude.ai/code/session_01Vc6LdYTvcSnCUo61MorWP6

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[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
constants/float16/ln-half	$\\color{green}50/50$ $\\color{green}+100.00\\%$	$\\color{green}1/1$ $\\color{green}+100.00\\%$	$\\color{green}0/0$ $\\color{green}+100.00\\%$	$\\color{green}50/50$ $\\color{green}+100.00\\%$

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