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

[Planeshifter]

Resolves a part of #11352.

Description

What is the purpose of this pull request?

This pull request:

• migrates the tests for math/base/special/betaincinv 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 delta/tol computation and the y === expected special case in test/test.js with a single t.strictEqual( isAlmostSameValue( y, expected[ i ], N ), true, 'returns expected value' ); assertion, using a named ULP constant declared at the top of each test body.
• removes the now-unused @stdlib/math/base/special/abs and @stdlib/constants/float64/eps requires and adds @stdlib/assert/is-almost-same-value.

ULP bounds (measured minima):

Test	Previous tolerance	ULP bound	Next largest ULP difference in set
lower regularized incomplete beta function	15.0 * EPS * abs( expected )	20	10
upper regularized incomplete beta function	15.0 * EPS * abs( expected )	14	13

Each bound is the smallest integer for which the corresponding fixture set (2000 points) passes in full, computed via @stdlib/number/float64/base/ulp-difference over every fixture point directly rather than by trial and error.

There is no test/test.native.js for this package, so only test/test.js is changed. No source, documentation, or package.json changes are included.

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:

• make test TESTS_FILTER=".*/math/base/special/betaincinv/.*" — 4020 passing, 0 failing (run twice at the final bounds with identical results, so the bounds are not sensitive to FMA/arch variation on this machine).
• Confirmed tightness: lowering either bound by 1 ULP (19 and 13) produces 2 failures.
• npx eslint on the changed file — clean.
• make lint-javascript-tests TESTS_FILTER=".*/math/base/special/betaincinv/.*" — clean.

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 candidate discovery (scanning the whole repo for the old tolerance idiom, then checking existing ULP-migration PRs to avoid collisions), the test migration, and the ULP bound search (computing the exact per-point ULP difference directly, then confirming determinism via repeated runs) were performed by the agent, following the idiom established in already-migrated packages in math/base/special (e.g. erfcinv, #13761, and bessely0, #14350).

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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/betaincinv	$\\color{green}133/133$ $\\color{green}+0.00\\%$	$\\color{green}14/14$ $\\color{green}+0.00\\%$	$\\color{green}1/1$ $\\color{green}+0.00\\%$	$\\color{green}133/133$ $\\color{green}+0.00\\%$

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