Improve Crossandra.tokenize return type

[trag1c]

Right now the method is declared to return list[Enum | Any] where:

• Enum refers to the token_source enum members (probably not specific to the one specified in the __init__?)
• Any refers to anything that the rules supplied to the tokenizer return

It feels like both things could be improved with generics.

Here are some (hopefully relevant) highlights of their origin:

def invert_enum(enum: type[Enum]) -> dict[str, Enum]:
    ...


class Empty(Enum):
    pass


class Crossandra:

    def __init__(
        self,
        token_source: type[Enum] = Empty,
        *,
        ...
        rules: list[Rule[Any] | RuleGroup] | None = None,
        ...
    ) -> None:
        self.__rules: list[Rule[Any]] = []
        for r in rules or []:
            if isinstance(r, RuleGroup):
                self.__rules.extend(r)
            else:
                self.__rules.append(r)
        ...
        self.__tokens = invert_enum(token_source)
        ...

    def tokenize(self, code: str) -> list[Enum | Any]:
        ...

Solving #16 is likely to help here.