Feature Request: Support Load & Store Trials about tpe HOT 2 CLOSED

let temp_file = tempfile::NamedTempFile::new()?;
let mut rng = rand::thread_rng();

fn objective(x: f64) -> f64 {
    x.powi(2)
}

{
    let mut optim =
        tpe::TpeOptimizer::new(tpe::parzen_estimator(), tpe::range(-5.0, 5.0)?);

    // Runs 100 trials.
    for _ in 0..100 {
        let x = optim.ask(&mut rng)?;
        let v = objective(x);
        optim.tell(x, v)?;
    }

    // Stores the trials.
    let mut file = std::fs::OpenOptions::new()
        .write(true)
        .open(temp_file.path())?;
    serde_json::to_writer(&mut file, &optim.trials().collect::<Vec<_>>())?;
}

{
    let mut optim =
        tpe::TpeOptimizer::new(tpe::parzen_estimator(), tpe::range(-5.0, 5.0)?);

    // Loads the previous trials.
    let mut file = std::fs::File::open(temp_file.path())?;
    let trials: Vec<(f64, f64)> = serde_json::from_reader(&mut file)?;
    for (x, v) in trials {
        optim.tell(x, v)?;
    }

    // Runs additional 100 trials.
    for _ in 0..100 {
        let x = optim.ask(&mut rng)?;
        let v = objective(x);
        optim.tell(x, v)?;
    }
    assert_eq!(optim.trials().count(), 200);
}