feat: Add retry with context

[Xuanwo]

Close #49

use anyhow::anyhow;
use anyhow::Result;
use backon::ExponentialBuilder;
use backon::RetryableWithContext;

struct Test;

impl Test {
    async fn hello(&mut self) -> Result<usize> {
        Err(anyhow!("not retryable"))
    }
}

#[tokio::main]
async fn main() -> Result<()> {
    let mut test = Test;

    // (Test, Result<usize>)
    let (_, result) = {
        |mut v: Test| async {
            let res = v.hello().await;
            (v, res)
        }
    }
    .retry(&ExponentialBuilder::default())
    .context(test)
    .await;

    Ok(())
}