libm

Kinogaki's own libm, published under the crates.io name so the frozen naga resolves to it through [patch.crates-io]. It is not upstream libm: it has only the four functions naga calls directly (its other float maths goes through our num-traits, which uses std).

• rint, rintf: round to the nearest integer, ties to even (exact).
• asinh, acosh: the classic argument-range split (as in fdlibm and musl) over std's ln, ln_1p and sqrt, so large arguments do not overflow and small ones keep their precision. Accuracy is checked against reference values computed to 40 digits (tests/accuracy.rs): within 1 ulp.