Function generate_synthetic_array 

pub fn generate_synthetic_array(cfg: SyntheticConfig) -> SyntheticDataset

Generate a synthetic sonobuoy array with class-conditional temporal events.

Buoys are placed on a rough grid. Roughly one third of nodes are labelled ambient / vessel / mammal. Vessel and mammal events are injected into the temporal buffer; neighbors share a weak bleed of the same event to make spatial aggregation informative.