Added RKN methods

[ParamThakkar123]

Checklist

• [x] Appropriate tests were added
• [x] Any code changes were done in a way that does not break public API
• [ ] All documentation related to code changes were updated
• [x] The new code follows the contributor guidelines, in particular the SciML Style Guide and COLPRAC.
• [ ] Any new documentation only uses public API

Additional context

Add any other context about the problem here.