Function py_kopf_kmatrix_rho 

pub fn py_kopf_kmatrix_rho(
    tags: &Bound<'_, PyTuple>,
    couplings: [[PyParameter; 2]; 2],
    channel: PyKopfKMatrixRhoChannel,
    mass: PyMass,
) -> PyResult<PyExpression>

Construct the fixed Kopf rho K-matrix amplitude.