Breaking change: `Reserved` now has one constructor instead of 4

Reserved{,Confl}{,Mut} are all removed and replaced by Reserved m cf where m := InteriorMut | TyFrz and cf := ResConflicted | ResActivable

The reachability statement is adapted with InteriorMut and TyFrz unreachable from each other, and ResActivable able to become ResConflicted but not the opposite.

This may be an opportunity to also simplify the transition function by merging similar cases, but not today.