Function compute_rmse 

pub fn compute_rmse(
    detected: &[[f64; 2]; 4],
    ground_truth: &[[f64; 2]; 4],
) -> f64

Compute RMSE corner error between detected and ground truth corners.

Unlike compute_corner_error, this does NOT try rotations - it assumes corners are already in the correct order. Use this when comparing against ground truth datasets with known corner ordering conventions.

Formula: sqrt( (sum of squared distances for all 4 corners) / 4 )