Function differential_expression 

pub fn differential_expression(
    counts: &[f64],
    n_genes: usize,
    n_samples: usize,
    condition: &[bool],
    method: DeMethod,
) -> Result<DeResults>

Run differential expression analysis on a count matrix.

• counts: row-major n_genes × n_samples count matrix.
• condition: boolean mask (true = treatment, false = control), one per sample.
• method: which test to apply.

Returns DeResults with genes sorted by ascending p-value.