float: pin erf/erfc(1.0) per platform libm

[brandonros]

`math_domains_and_live_pg_values` fails on every macOS checkout: Apple's libm differs from glibc by one ulp at `erf(1.0)` and `erfc(1.0)`. Pin both arms by `target_os` so a libm regression on either platform is still caught, the way the existing `lgamma` arms already do.

Verified: `cargo test -p adt_float math_domains` passes on Darwin 25.6.

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Summary by CodeRabbit

• Tests
  • Updated mathematical accuracy tests to account for minor platform-specific differences in erf(1.0) and erfc(1.0) results on macOS versus other operating systems.

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

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Run ID: 481dc079-5ddb-4133-8043-33989920df5d

📥 Commits

Reviewing files that changed from the base of the PR and between 4c2e49f and 88f7aa2.

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• crates/backend/utils/adt/float/src/tests.rs

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📝 Walkthrough

Walkthrough

The float math test now uses target-specific expected values for erf(1.0) and erfc(1.0). macOS uses values that differ by one ulp from the values used on other platforms.

Changes

Float assertion portability

Layer / File(s)	Summary
Platform-specific erf assertions crates/backend/utils/adt/float/src/tests.rs	The test uses macOS-specific expected values and retains the existing values for non-macOS targets. A comment documents the libm difference.

Estimated code review effort: 1 (Trivial) | ~3 minutes

Merge Risk: ⚪ Minimal · up to 88f7a

This updates float-test expectations for the documented one-ULP macOS libm difference while retaining the existing values elsewhere. No production behavior changes, and the change is ready to merge.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the platform-specific pinning of erf(1.0) and erfc(1.0) test values, which is the main change.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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