Function with_retry 

pub async fn with_retry<F, Fut, T, E>(
    policy: &RetryPolicy,
    op: F,
) -> Result<T, E>
where
    F: FnMut() -> Fut,
    Fut: Future<Output = Result<T, E>>,
    E: Display,

Execute an async operation with the given retry policy (all errors are considered retryable).