[Code scan] Fix Batch.num_graphs for NumPy ptr arrays

[njzjz]

This issue comes from a Codex global repository scan.

Problem

Batch.num_graphs calls self.ptr.numel(), but this NumPy batch implementation stores ptr as a NumPy array:

dftio/dftio/data/batch_np.py

Lines 275 to 283 in c9d128f

	@property
	def num_graphs(self) -> int:
	"""Returns the number of graphs in the batch."""
	if self.__num_graphs__ is not None:
	return self.__num_graphs__
	elif self.ptr is not None:
	return self.ptr.numel() - 1
	elif self.batch is not None:
	return int(self.batch.max()) + 1

NumPy arrays do not have .numel(), so Batch(ptr=np.array([0, 2, 5])).num_graphs raises AttributeError.

Suggested fix

Use a NumPy/Python length API, for example:

return len(self.ptr) - 1