simulator() docstring names the wrong return key ('responses' vs 'choices') and a nonexistent 'deadline' argument

[AlexanderFengler]

The simulator() docstring (ssms/basic_simulators/simulator.py) describes a
return dict with keys 'rts', 'responses', 'metadata' (lines ~671 and ~690).
The actual key is 'choices' — as used internally at simulator.py:489,
:816, :819.

The same docstring documents a deadline parameter (lines ~645-646) that is not
in the signature; deadline models are selected via the _deadline model-name
suffix instead.

Reproducer

import inspect
from ssms.basic_simulators.simulator import simulator

out = simulator(theta=[0.5, 1.2, 0.5, 0.3], model="ddm", n_samples=10)
print("documented keys :", "['rts', 'responses', 'metadata']")
print("actual keys     :", sorted(out.keys()))
print("'responses' present?", "responses" in out)
print("'deadline' in signature?", "deadline" in inspect.signature(simulator).parameters)

documented keys : ['rts', 'responses', 'metadata']
actual keys     : ['binned_128', 'binned_256', 'choice_p', 'choice_p_no_omission',
                   'choices', 'go_p', 'metadata', 'nogo_p', 'omission_p', 'rts']
'responses' present? False
'deadline' in signature? False

Documentation-only fix, but it is the first thing a new user reads.

Version: ssm-simulators 0.13.2

[linear-code]

HSSM-697