pub trait CalculatorProxyInterface: Send + Sync {
type AddResponseFut: Future<Output = Result<f64, Error>> + Send;
type SubtractResponseFut: Future<Output = Result<f64, Error>> + Send;
type MultiplyResponseFut: Future<Output = Result<f64, Error>> + Send;
type DivideResponseFut: Future<Output = Result<f64, Error>> + Send;
type PowResponseFut: Future<Output = Result<f64, Error>> + Send;
// Required methods
fn add(&self, a: f64, b: f64) -> Self::AddResponseFut;
fn subtract(&self, a: f64, b: f64) -> Self::SubtractResponseFut;
fn multiply(&self, a: f64, b: f64) -> Self::MultiplyResponseFut;
fn divide(&self, dividend: f64, divisor: f64) -> Self::DivideResponseFut;
fn pow(&self, base: f64, exponent: f64) -> Self::PowResponseFut;
}