Allow typing from missing dependency

[ZanSara]

Problem

In Haystack we often need to type method signatures with missing dependencies. Something like:

import numpy as  np
import torch

def my_complicated_function(device: Optional[torch.device]) -> Union[torch.tensor, np.ndarray]:
    ...

I found that torch.device, torch.tensor and np.ndarray trigger generalimport once wrapped in a container like Optional or Union, while they don't when they're unwrapped, like:

import numpy as  np
import torch

def my_complicated_function(device: torch.device) -> torch.tensor, np.ndarray:
    ...

Solution

I found that adding __args__ = [] in FakeModule seems to fix the issue. I'm going to open a small PR for this case.