test: migrate stats/base/dists/f/cdf to ULP-based testing

[DivyanshuVortex]

Resolves a part of #11352.

Description

What is the purpose of this pull request?

This pull request:

• migrates the tests for stats/base/dists/f/cdf from relative tolerance testing to ULP difference testing, per [RFC]: Migrate math/base/special packages from relative tolerance testing to ULP difference testing (tracking issue) #11352.
• replaces the y === expected[i] / delta <= tol branch in the Julia fixture loops of test/test.cdf.js and test/test.factory.js with t.strictEqual( isAlmostSameValue( y, expected[ i ], N ), true, 'returns expected value' );.
• adds the @stdlib/assert/is-almost-same-value require and drops the now unused @stdlib/math/base/special/abs and @stdlib/constants/float64/eps requires.

Final ULP constants (per fixture, identical across both test files):

• both_large.json: 58 ULP (replaces 50.0 * EPS)
• large_d1.json: 542 ULP (replaces 400.0 * EPS)
• large_d2.json: 171 ULP (replaces 200.0 * EPS)

These bounds were determined empirically by measuring the maximal ULP difference across the full 1000-element Julia fixture sets.

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.

Test results via make test TESTS_FILTER=".*/stats/base/dists/f/cdf/.*": test.cdf.js 3019 passing, test.factory.js 3022 passing, test.js 3 passing; 0 failing. All files have been updated to cleanly adhere to the new ULP guidelines without any unused variables left behind.

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

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• 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 with the help of an AI coding assistant (Gemini)

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Coverage Report

Package	Statements	Branches	Functions	Lines
stats/base/dists/f/cdf	$\\color{green}253/253$ $\\color{green}+100.00\\%$	$\\color{green}31/31$ $\\color{green}+100.00\\%$	$\\color{green}3/3$ $\\color{green}+100.00\\%$	$\\color{green}253/253$ $\\color{green}+100.00\\%$

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