Function expand_with 

pub fn expand_with<B, G, P, S>(bounds: &mut B, geometry: &G, strategy: S)
where
    B: BoxTrait<Point = P>,
    G: Geometry<Point = P>,
    P: PointMut + Default,
    S: EnvelopeStrategy<G, Output = Box<P>>,

Expand bounds using an explicitly supplied envelope strategy.

Mirrors the strategy overload of boost::geometry::expand from algorithms/detail/expand/interface.hpp:135-153. Returning an envelope from the strategy keeps the mutation generic over any writable Box concept implementation.