Function retry_async 

pub async fn retry_async<T, Fut>(
    policy: &RetryPolicy,
    should_retry: impl Fn(&Error) -> bool,
    op: impl FnMut() -> Fut,
) -> Result<T>
where
    Fut: Future<Output = Result<T>>,

Run op, retrying its result while should_retry says so and policy has attempts left, sleeping the (jittered, exponential) backoff between tries. The op is re-invoked from scratch each attempt, so it must be idempotent for the errors should_retry selects (lock-contention failures are — the command never ran). Returns the first Ok, or the last Err.