Function check_completely_positive 

pub fn check_completely_positive<R>(
    choi: &CausalTensor<Complex<R>>,
    tol: R,
) -> Result<(), QuantumError>
where
    R: RealField + FromPrimitive + Default + Debug,

Complete positivity check: E is CP iff its Choi operator is PSD (spectrum ≥ −tol via the Hermitian eigendecomposition).

Decides and discards. The sibling check_completely_positive_report keeps the defect and the spectrum it computed.