Function pca_init 

pub fn pca_init(
    data: &[f32],
    n: usize,
    d: usize,
) -> Result<Vec<[f32; 2]>, PaCMAPError>

Project n × d row-major data onto its top 2 principal components.

Returns n (x, y) pairs where x and y are the PC1 and PC2 scores, normalised to the range used by the paper’s initialisation.