async-std's future timeout helper is too inflexible about errors

[Fishrock123]

The async_std::futures::timeout helper would be much more useful if it was generic over Error and took a callback closure to be called when a timeout is hit, so that one can construct /map to their own error type.

[jbr]

How would that be preferable to

#[async_std::main]
pub async fn main() -> Result<(), &'static str> {
    async_std::future::timeout(std::time::Duration::from_secs(1), std::future::pending())
        .await
        .map_err(|_| "timed out")
}

[Fishrock123]

Completely avoids unnecessary error context loss due to error translations.