Allow `.context` to be called on a future that returns result without awaiting.

trait.rs

use std::error::Error;
use std::result::{Result as StdResult};
use anyhow::{Context, Result};

trait FutureExt<O> {
    async fn context(self, ctx: &'static str) -> Result<O, anyhow::Error>;
}

impl<T, O, E> FutureExt<O> for T
where
    T: Future<Output = StdResult<O, E>>,
    E: Error + Send + Sync + 'static,
{
    async fn context(self, ctx: &'static str) -> Result<O> {
        self.await.context(ctx)
    }
}