Function cast_decimal_to_f64 

fn cast_decimal_to_f64<D, F>(
    array: &dyn Array,
    as_float: &F,
    scale: i8,
) -> Result<ArrayRef, ArrowError>
where
    D: DecimalType + ArrowPrimitiveType,
    F: Fn(D::Native) -> f64,

Casts a decimal array to Float64, rounding each value once.