Function surface_signed_delta_from_strike 

pub fn surface_signed_delta_from_strike(
    market: &SurfaceMarketContext,
    expiry: SurfaceTenor,
    strike: f64,
    option_type: OptionType,
    volatility: f64,
    model: PricingModel,
    convention: SurfaceDeltaConvention,
) -> Result<f64, FerroRiskError>