Function hermite_function_series_slice 

pub fn hermite_function_series_slice<P, E, V, const EXACT_FMA: bool>(
    x: V,
    coeffs: &[E],
) -> V
where
    P: Policy,
    E: FloatElement,
    V: FloatVector<Element = E> + SpecializedTranscendentalMath<E>,

Runtime-length form of hermite_function_series.

A genuine port of the recurrence rather than a fold over the const kernel: a series carries k-dependent state and does not partition the way the slice reductions in thermite do. Both forms must be edited together.

Same pre-scaling by f, same seed, same final factor. Read hermite_function_series for why the split is there. The runtime length costs the unrolling and turns a_k, b_{k+1} into per-step square roots of a ratio rather than folded literals, which is the expensive part here.

The empty series is 0, where the const form refuses to compile.