Consider having current attempt number sent as a closure argument

[olekspickle]

Is your feature request related to a problem? Please describe.
Sometimes you want to know what is going on and more detailed logs can be useful

Describe the solution you'd like
A current attempt passed as a closure argument:

tryhard::retry_fn(|n| ...)

Describe alternatives you've considered
Of course you can always have let mut attempt = 0, but it is not really idiomatic, is it? :)

Additional context
Illustrative example:

use tryhard; // 0.5.0
use std::time::Duration;

async fn call(n: u8) -> Result<String, String> {
    if n > 5 {
        Ok("Ok, move along".to_string())
    }else {
        Err("You shall not pass".to_string())
    }
}

#[tokio::main]
async fn main() {
    let mut attempt = 0;
    let s = tryhard::retry_fn(|| async {
        attempt += 1;
        println!("Once more into the fray, attempt: {attempt}");
        call(attempt).await
    })
        .retries(6)
        .exponential_backoff(Duration::from_secs(1))
        .max_delay(Duration::from_secs(10))
        .await;
    
    println!("{s:?}");
}