Remove assertion forbidding composition in __new__

Author: ValerianRey

src/torchjd/sparse/_structured_sparse_tensor.py

@@ -14,10 +14,6 @@ class StructuredSparseTensor(Tensor):
 
     @staticmethod
     def __new__(cls, physical: Tensor, strides: Tensor):
-        # At the moment, this class is not compositional, so we assert
-        # that the tensor we're wrapping is exactly a Tensor
-        assert type(physical) is Tensor
-
         assert strides.dtype == torch.int64
 
         # Note [Passing requires_grad=true tensors to subclasses]