Minor rt fixes
Minor fixes before we get into getting RT to run correctly with the new multiscale particle interactions (h_max_active stuff).
- added const qualifiers to function parameters so code compiles.
- limit h_max in toy RT example so run starts.
This should close #912 (closed) . @tkchan , note that RT in the main branch is still not usable in the moment due to the new multiscale particle interactions.