Function estimate_coverage 

pub fn estimate_coverage(
    centers: &[SphericalPoint],
    half_angles: &[f64],
    num_samples: usize,
) -> CoverageReport

Estimates sphere coverage via Monte Carlo sampling.

Each “cap” is (center, half-angle). A sample is “covered” if it falls within at least one cap. Accuracy ~ O(1/√num_samples).