refactor: add_to_nfa.

[SharafMohamed]

Request

add_to_nfa should explicitly take as arguments the source and dest states.

Possible implementation

auto add_to_nfa(finite_automata::RegexNFA<NFAStateType>* nfa, NFAStateType* source, NFAStateType* dest) const -> void;

• For void RegexASTMultiplication<NFAStateType>::add_to_nfa the implementation can also be refactored here to make better use of epsilon transitions. We can also disable the min==0 case as these are disallowed in TNFAs.