Function mutual_information_bytes 

pub fn mutual_information_bytes(x: &[u8], y: &[u8], max_order: i64) -> f64

Compute mutual information I(X;Y) = H(X) + H(Y) - H(X,Y).

Dispatches based on max_order. If 0, uses marginals; else uses rates.

I(X;Y) = Σ p(x,y) log(p(x,y) / (p(x)p(y)))