feat: start of lift, debugging, cleanup

src/lib/solvers/statefulRK45.ml

@@ -22,6 +22,8 @@ module Functional =
         { state; vec = init } in
 
       let step ({ state ; vec=v } as s) h =
+        Common.Debug.print "SOLVER STEP";
+        Common.Debug.print_entry v;
         let y_nv = vec v in
         let h = step state h y_nv in
         let state = copy state in