Add NotImplementedError in einsum

Author: ValerianRey

src/torchjd/sparse/_aten_function_overrides/einsum.py

@@ -11,6 +11,7 @@
 
 
 def einsum(*args: tuple[StructuredSparseTensor, list[int]], output: list[int]) -> Tensor:
+    raise NotImplementedError()
 
     # First part of the algorithm, determine how to cluster physical indices as well as the common
     # p_shapes corresponding to matching v_dims. Second part translates to physical einsum.