test: migrate stats/base/dists/weibull/pdf 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 stats/base/dists/weibull/pdf from relative tolerance testing (delta <= N * EPS * abs( expected )) to ULP difference testing using @stdlib/assert/is-almost-same-value.

The following files are updated, each containing the same three Julia fixture loops:

File	both_large.json	large_scale.json	large_shape.json
test/test.pdf.js	0	0	0
test/test.factory.js	0	0	0
test/test.native.js	0	0	0

Each bound is the measured minimum over the full fixture set (1000 cases per fixture, 3000 cases per file). 0 is the tightest bound the assertion admits: at 0, isAlmostSameValue reduces to the SameValue algorithm, so every returned value matches its Julia-generated expected value bit-for-bit, and no case relies on any tolerance. The previous relative tolerances (1.0 * EPS, and 2.0 * EPS for one loop in test/test.native.js) were therefore never exercised.

The JavaScript, factory, and C implementations were each measured independently and agree exactly on all three bounds, so a single set of values is used across the three files.

Only the three test files are changed; no implementation, documentation, or fixture files are touched.

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.

Verification performed locally:

test.js          3 passing
test.pdf.js      3023 passing
test.factory.js  3028 passing
test.native.js   3023 passing

eslint --config etc/eslint/.eslintrc.tests.js (all four test files)
  clean

The native add-on was built locally so that test/test.native.js actually executed rather than being skipped. The full suite was run twice at the final bounds to confirm the results are deterministic, and the add-on was additionally rebuilt with CFLAGS="-ffp-contract=off" to confirm the C bounds are not sensitive to FMA contraction (identical bounds in both builds).

Note on the local environment: make install-node-modules could not complete in the sandbox used to author this change, because a transitive development dependency resolves to es-object-atoms@^1.1.2, which is not published on the registry. The test runner, ESLint (with the project's .eslintrc.tests.js configuration and the stdlib plugin), and node-gyp were installed separately so that the checks above could be run; the editorconfig-checker and production license pre-commit/pre-push hooks could not run, since both fetch artifacts that are unreachable from the sandbox. EditorConfig conformance for the three changed files (LF endings, UTF-8, tab indentation, no trailing whitespace, final newline) was verified manually instead.

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 authored by Claude Code running as an unattended scheduled task. The agent studied previously merged conversions under this tracking issue (in particular the sibling package stats/base/dists/weibull/cdf) to match the established idiom, applied the migration, and determined the minimum ULP bounds empirically by computing the exact per-element ULP distance across the fixture set for the JavaScript, factory, and native implementations.

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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/weibull/pdf	$\\color{green}310/310$ $\\color{green}+100.00\\%$	$\\color{green}36/36$ $\\color{green}+100.00\\%$	$\\color{green}4/4$ $\\color{green}+100.00\\%$	$\\color{green}310/310$ $\\color{green}+100.00\\%$

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