Rework the architecture

[bygu4]

Here we plan to rework the architecture of Pyformlang library, removing cyclic imports and hopefully making the design clearer. That would further allow us to add type annotations for most of the code, improving its rigor and readability as well as the interface of the project. For more detail, see issues:

• Issues with finite_automaton architecture #25,
• General architecture improvement #26.

[bygu4]

Rework several modules and their relations with adding type annotations. The following modules were affected:

• finite_automaton,
• regular_expression,
• rsa,
• cfg,
• pda.

In more detail, we can describe the changes as follows.

finite_automaton:

• Refactor automata transformations, including to_deterministic and remove_epsilon_transitions methods.
• Move from_networkx to EpsilonNFA.
• Rework transition functions of automata, adding DeterministicTransitionFunction class and TransitionFunction abstract class.
• Refactor automata copying, add missing copy method for NFA.
• Make FiniteAutomaton an abstract class.
• Remove Regexable interface, implement automata union, concatenation and kleene star manually.
• Add more methods for finite automata, including get_transitions_from, get_next_states_from, etc.
• Add utils file for containing finite automata utility.

regular_expression:

• Refactor automata to regex transformations, build regex from automata in Regex class.
• Add copying of ENFA in to_epsilon_nfa method.
• Add to_minimal_dfa method to Regex for using in recursive automata.

rsa:

• Correct some properties and type annotations.

cfg and pda:

• Define intersection with DFA explicitly.

[bygu4]

@Aunsiels
Please check out the following requests as well:

1. Rework cfg FormalLanguageConstrainedPathQuerying/pyformlang#14 --- continue adding type annotations and refactoring;
2. Rework indexed grammars FormalLanguageConstrainedPathQuerying/pyformlang#15 --- finish refactoring and adding annotations, add pyright to CI;
3. Update documentation FormalLanguageConstrainedPathQuerying/pyformlang#16 --- set up Ruff, format and update all of the docstrings.

I would suggest creating a separate branch where we can try merging all of that