pub fn build_projection(shape: PredictorShape, seed: u64) -> Vec<bf16>Expand description
2026-09-25: Random Gaussian projection P, [head_dim, r] row-major BF16, from a
ChaCha8 stream seeded with seed. Entries have variance 1 / head_dim, so for a
key k a projected coordinate has variance |k|^2 / head_dim.