Changes to support running the client under future annotations

[brunomlopes]

Hi,

I've been trying to work with the python dtos for a large project, and found some issues with the client.

These changes below seem to be needed for some of the cases.
The generated code also needed to be corrected, to pull some classes to the top of the file, before they are referenced.

These changes were done to support self-referencial type annotations in python 3.11 (via from future import annotations ).
Not sure if they are correct.

The main scenarios are things like:

@dataclass_json(letter_case=LetterCase.CAMEL, undefined=Undefined.EXCLUDE) @dataclass
class PagedResults:
    current_page: int = 0
    total_results: int = 0
    page_size: int = 0

T = TypeVar('T')

@dataclass_json(letter_case=LetterCase.CAMEL, undefined=Undefined.EXCLUDE) @dataclass
class PagedResults1(Generic[T], PagedResults):
    results: Optional[List[T]] = None

@dataclass_json(letter_case=LetterCase.CAMEL, undefined=Undefined.EXCLUDE) @dataclass
class AResponseWithPagedResults:
    paged_results: Optional[PagedResults1[SomeDto]] = None

@dataclass_json(letter_case=LetterCase.CAMEL, undefined=Undefined.EXCLUDE) @dataclass
class HierarchicalDto:
    children: Optional[List[HierarchicalDto]] = None

[mythz]

great, thx for the PR!