Add batch-evaluate mode

[contramundum53]

Kurobako has evaluate subcommand that evaluates a problem at a given set of params. However, when we want to repeatedly evaluate different sets of params and the problem needs to load a large dataset, this is inefficient because the problem reloads the dataset every time. We add batch-evaluate subcommand that uses stdio to repeatedly evaluate sets of params without reloading the process.

[coveralls]

Pull Request Test Coverage Report for Build 2961163548

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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Details

• 0 of 41 (0.0%) changed or added relevant lines in 2 files are covered.
• 258 unchanged lines in 8 files lost coverage.
• Overall coverage decreased (-0.02%) to 9.487%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/main.rs	0	4	0.0%
src/batch_eval.rs	0	37	0.0%

Files with Coverage Reduction	New Missed Lines	%
../../../.cargo/registry/src/github.com-1ecc6299db9ec823/trackable-0.2.23/src/macros.rs	5	0.0%
../../../.cargo/registry/src/github.com-1ecc6299db9ec823/ndarray-0.12.1/src/error.rs	6	0.0%
kurobako_core/src/registry.rs	8	0.0%
kurobako_core/src/trial.rs	10	0.0%
kurobako_problems/src/sigopt.rs	40	0.0%
src/plot/slice.rs	45	0.0%
src/plot/pareto_front.rs	46	0.0%
src/plot/curve.rs	98	0.0%

Totals
Change from base Build 2668460033:	-0.02%
Covered Lines:	1092
Relevant Lines:	11510

---

💛 - Coveralls

[sile]

I think that we can use kurobako_core::json::load() function (https://github.com/optuna/kurobako/blob/master/kurobako_core/src/json.rs#L19) to read parameters from the stdin until it reaches EOS.
IMO, the load function is simpler than MessageReceiver for this purpose and, by using the load function, we could remove BatchEvaluateMessage enum as it would be sufficient to define a minimum struct like the following:

#[derive(Deug, Deserialize)]
struct EvalCall {
    params: Params,
    step: Option<u64>
}

impl BatchEvaluateOpt {
    pub fn run(&self) -> Result<()> {
        let calls: Vec<EvalCall> = track!(kurobako_core::json::load(io::stdin()))?;
        ...
    }
}

[sile]

FYI: I just created #48 to fix CI (lint) failure.

[HideakiImamura]

LGTM.

[HideakiImamura]

Let me merge this PR with my one approval since we need this feature.