Implement from_dir

@dataclass(frozen=True, eq=False)

class PaymentOrderCollection(Iterable[PaymentOrder]):

    base_dir: Path

    orders: tuple[PaymentOrder, ...]

    @classmethod

    def get(cls, studienfachschaft: Studienfachschaft, year: int) -> Self:

    @classmethod

    def from_dir(cls, path_or_str: Path | str) -> Self:

        pass  # TODO

        return cls(

            tuple(

                load_pdf(pdf) for pdf in Path(path_or_str).rglob("*.pdf")

            )

        )

    def __iter__(self) -> Iterator[PaymentOrder]:

        return (load_pdf(pdf) for pdf in self.base_dir.rglob("*.pdf"))

        return iter(self.orders)

    @property

    def by_budgetary_item_id(self):