Fix missing type hint

Author: ValerianRey

src/torchjd/autogram/_gramian_computer.py

@@ -4,6 +4,8 @@
 from torch import Tensor
 from torch.utils._pytree import PyTree
 
+from torchjd.autogram._jacobian_computer import JacobianComputer
+
 
 class GramianComputer(ABC):
     @abstractmethod
@@ -24,7 +26,7 @@ def reset(self):
 
 
 class JacobianBasedGramianComputer(GramianComputer, ABC):
-    def __init__(self, jacobian_computer):
+    def __init__(self, jacobian_computer: JacobianComputer):
         self.jacobian_computer = jacobian_computer
 
     @staticmethod