Fix _print_signature() for verbose=True

[Winston-503]

Fix the following error:

[/usr/local/lib/python3.10/dist-packages/dspy/teleprompt/signature_opt.py](https://localhost:8080/#) in _print_signature(self, predictor)
     96                 signature = predictor.extended_signature1
     97             # print(f"i: {signature.instructions}")
---> 98             # print(f"p: {list(signature.fields().values())[-1].json_schema_extra['prefix']}")
     99             print()
    100 

TypeError: 'dict' object is not callable

for Signature Optimizer example. Also, compiled_prompt_opt = teleprompter.compile(cot, devset=devset, eval_kwargs=kwargs) should be changed to compiled_prompt_opt = teleprompter.compile(cot_baseline, devset=devset, eval_kwargs=kwargs)

[arnavsinghvi11]

Thanks @Winston-503 ! Looks like this matches the same fix as #547 which is now merged :). Feel free to close if that's correct!

[Winston-503]

Yes, looks like it, thanks.