Prevent changing the state 0 of a DFA.

[marfvr]

Is your feature request related to a problem? Please describe.

When the DFA is built incrementally, the library should prevent any change to the state 0, that is:

• cannot be set as a final state
• cannot add a transition from it

Notice: transitions to state 0 are already present by default, because the BDDs for each bit only store the transitions that lead to positive bits.

Describe the solution you'd like n/a

Describe alternatives you've considered n/a

Additional context n/a