Fix predict usage tracking

[chenmoneygithub]

fix #8145

It actually indicates a bigger problem that our dspy.Predict's __call__ is not using the Module.__call__. We override the __call__ in dspy.Predict to disallow positional args, but it should still utilize the parent's __call__.

We also improve the error message on users passing positional args to dspy.Predict.

Before:

TypeError: Predict.__call__() takes 1 positional argument but 2 were given

After:

ValueError: Positional arguments are not allowed when calling `dspy.Predict`, must use keyword arguments that match your signature input fields. For example: dspy.Predict('question -> answer')(question='What is the capital of France?')