Add stream functions to the Sampler interfaces

public interface ContinuousDistribution {

    // ...

    Sampler createSampler(UniformRandomProvider rng);

    /**
     * Sampling functionality.
     */
    interface Sampler {
        double sample();

        default DoubleStream samples() {
            return DoubleStream.generate(this::sample).sequential();
        }

        default DoubleStream samples(long streamSize) {
            return samples().limit(streamSize);
        }
    }
}

UniformRandomProvider rng = ...;
double[] x = NormalDistribution.of(1.23, 4.56)
                               .createSampler(rng)
                               .samples(100)
                               .toArray();