Dataclass

* current version : c538fae
* Is it desirable to use a `dataclass` to implement a state space model?
* ref : https://www.daleseo.com/python-dataclasses/
* Additionally, is a `numpy.ndarray` safe as one of initial values? [code](https://github.com/kangwonlee/nmisp/blame/c538fae443da0505c87908e03e6d100b22a26ec4/50_ode/35_Runge_Kutta_Higher_Order.ipynb#L324) Do different instances share one same `ndarray` ?

Start by reviewing the state-space-related code in 50_ode/35_Runge_Kutta_Higher_Order.ipynb, especially the code around line 324, and consult the linked dataclasses reference. Determine whether dataclass use is appropriate and whether initial numpy.ndarray values are shared between instances; done means the project has a clear decision and corresponding implementation guidance.

Written by the indexing model from the issue text.