Function st_buffer 

pub fn st_buffer(
    geom: &Geometry,
    distance_meters: f64,
    segments: usize,
) -> Geometry

ST_Buffer(geom, distance_meters) → Polygon.

Expands geometry by distance using equirectangular approximation.

• Point → 32-sided circle polygon
• LineString → buffered corridor (parallel offset + end caps)
• Polygon → expanded polygon (vertex offset outward)

Meter-to-degree conversion: Δlng = meters / (111320 * cos(lat)), Δlat = meters / 110540. Accurate to <0.5% for ±70° latitude.