Function cosine_similarity 

pub fn cosine_similarity(a: &[f32], b: &[f32]) -> f32

Compute cosine similarity between two f32 slices.

Returns a value in [0, 1] (mapped from raw [-1, 1] via (sim + 1) / 2). Returns 0.0 for empty, mismatched-length, or zero-norm vectors. Non-finite values (NaN, Inf) are treated as 0.0 per element.