Function forward_push_with_residuals 

pub fn forward_push_with_residuals(
    matrix: &CsrMatrix<f64>,
    source: usize,
    alpha: f64,
    epsilon: f64,
) -> Result<(Vec<f64>, Vec<f64>), SolverError>

Compute the estimate and residual vectors simultaneously.

Returns (estimate, residual) as dense Vec<f64> for use by hybrid random-walk algorithms that need to inspect residuals.