Fix mixed OrderedFloat equality for NaN values

[RanaPriyansh]

Problem

OrderedFloat<T> == T used primitive equality, so NaN values compared unequal despite the wrapper equality contract.

Change

Reuse OrderedFloat<T> equality for mixed equality.

Add f32 and f64 regression tests for NaN payloads, finite values, infinities, signed zero, and inequality.

Verification

• cargo fmt --check
• cargo test
• cargo test --no-default-features
• cargo test --no-default-features --features libm
• cargo test --features std,schemars
• cargo test --features rand,randtest
• cargo test --features arbitrary,bytemuck,rand,randtest,serde,schemars,proptest,rkyv,rkyv_ck,speedy,facet
• cargo clippy --tests --features arbitrary,bytemuck,rand,randtest,serde,schemars,proptest,rkyv,rkyv_ck,speedy,facet

All checks pass with Rust 1.94.1.

This change does not add mixed PartialOrd or reverse-comparison APIs.

Related to #143. This addresses the equality discrepancy only.

The Rust 1.90 CI job has not been run locally.

[mbrubeck]

I'm slightly concerned about the silent behavior change here, though I can't think of a likely scenario where it causes a problem.

Is this a high priority fix for anyone? If not, perhaps it should wait a while to see if we have a chance to bundle it into a new major version.

[RanaPriyansh]

Waiting for a major release makes sense. This PR addresses an equality consistency issue. I do not have evidence of urgent downstream impact.