Allow diffusers to load with Flax, w/o PyTorch (#6272)

Author: pcuenca

src/diffusers/utils/torch_utils.py

@@ -89,7 +89,7 @@ def is_compiled_module(module) -> bool:
     return isinstance(module, torch._dynamo.eval_frame.OptimizedModule)
 
 
-def fourier_filter(x_in: torch.Tensor, threshold: int, scale: int) -> torch.Tensor:
+def fourier_filter(x_in: "torch.Tensor", threshold: int, scale: int) -> "torch.Tensor":
     """Fourier filter as introduced in FreeU (https://arxiv.org/abs/2309.11497).
 
     This version of the method comes from here:
@@ -121,8 +121,8 @@ def fourier_filter(x_in: torch.Tensor, threshold: int, scale: int) -> torch.Tens
 
 
 def apply_freeu(
-    resolution_idx: int, hidden_states: torch.Tensor, res_hidden_states: torch.Tensor, **freeu_kwargs
-) -> Tuple[torch.Tensor, torch.Tensor]:
+    resolution_idx: int, hidden_states: "torch.Tensor", res_hidden_states: "torch.Tensor", **freeu_kwargs
+) -> Tuple["torch.Tensor", "torch.Tensor"]:
     """Applies the FreeU mechanism as introduced in https:
     //arxiv.org/abs/2309.11497. Adapted from the official code repository: https://github.com/ChenyangSi/FreeU.