test: migrate math/base/special/atandf to ULP-based testing

[Planeshifter]

Resolves a part of #11352.

Description

This pull request migrates test/test.js and test/test.native.js of math/base/special/atandf from relative-tolerance (EPS-based) assertions to ULP-difference assertions via @stdlib/number/float32/base/assert/is-almost-same-value, following the merged precedent for single-precision packages (e.g. math/base/special/hypotf, PR #12808).

• Replaces the delta/tol/EPS/absf-based tolerance checks in both the "negative values" and "positive values" test cases with t.strictEqual( isAlmostSameValue( y, e, 1 ), true, 'returns expected value' ).
• Removes the now-unused absf and EPS requires; keeps the existing float64ToFloat32 coercion of fixture expected values (unchanged from before).
• Minimum required ULP value: 1 for both the JavaScript and native implementations, verified by direct ULP-difference computation over both fixture files (negative.json, positive.json; combined 4009 assertions). The native add-on was built locally (make install-node-addons NODE_ADDONS_PATTERN=atandf) and its outputs were independently checked for max ULP difference against the fixtures (native negative: 1, native positive: 1; JS negative: 1, JS positive: 1).
• Ran the full test suite for the package twice (make test TESTS_FILTER=".*/math/base/special/atandf/.*") at ULP=1 to confirm deterministic passing (4009/4009 both runs, both files).
• npx eslint is clean on both changed files.
• No other files were changed.

Related Issues

• [RFC]: Migrate math/base/special packages from relative tolerance testing to ULP difference testing (tracking issue) #11352

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Disclosure

This PR was authored by an automated Claude Code agent running as a scheduled task, following the conventions established in prior merged ULP-migration PRs for this issue (e.g. #12808, #12799).

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Coverage Report

Package	Statements	Branches	Functions	Lines
math/base/special/atandf	$\\color{green}193/193$ $\\color{green}+100.00\\%$	$\\color{green}5/5$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}193/193$ $\\color{green}+100.00\\%$

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