Function openvino.core.custom_gradient() should be a class

[JulianJvn]

I'm not using this, but I saw by accident while browsing the code that keras.backend.openvino.core.custom_gradient() is a function that defines nested functions __init__() and __call__(), but doesn't do anything (in particular, it seems to return None):

keras/keras/src/backend/openvino/core.py

Lines 598 to 617 in c03ae35

	def custom_gradient(fun):
	"""Decorator for custom gradients.
	Args:
	fun: Forward pass function.
	"""
	def __init__(self, fun):
	warnings.warn(
	"`custom_gradient` for the openvino backend"
	" acts as a pass-through to "
	"support the forward pass."
	" No gradient computation or modification "
	"takes place."
	)
	self.fun = fun
	def __call__(self, *args, **kwargs):
	outputs, _ = self.fun(*args, **kwargs)
	return outputs

I think line 598 should be

class custom_gradient:

Introduced by 5c401a9 in #19727. It was a function throwing a NotImplementedError before, but should have been changed to a class.