NEXT VERSION:
- solver: improve logic. check after each dr?
- add checks for sequences >255 moves
- cat!
- niss for direct DR
  - prune for CO using CO+CP state
- Option: exactly N moves (or lower bound); exactly optimal?
- CO (also from EO), direct corners solve
- scramble shortner (solve + invert)
- RUF-ify

FUTURE IDEAS:
- sort before branching dfs