Function estimate_yaw_from_landmarks 

pub fn estimate_yaw_from_landmarks(landmarks: &[(f32, f32); 5]) -> f32

Estimate yaw angle (degrees) from 5-point SCRFD landmarks.

Uses the nose offset from the eyes-midpoint, normalised by inter-ocular distance. Positive = right-facing, negative = left-facing. The absolute value indicates how far the face is turned from frontal.