Docstring example for a fully custom simulator raises AxisError

[AlexanderFengler]

The "Fully custom simulator" example in the Simulator class docstring
(ssms/basic_simulators/simulator_class.py) raises when run verbatim.

The example returns 1-D rts/choices, but Simulator.simulate() calls
np.squeeze(x["rts"], axis=1) (simulator_class.py:675), which requires a
second axis.

This matters more than a typical docstring slip because it is the documented
entry point for the "bring your own model" workflow, and it is copy-pasteable.

Reproducer

import numpy as np
from ssms.basic_simulators.simulator_class import Simulator

# verbatim from the docstring
def my_sim(v, a, z, t, max_t=20, n_samples=1000, **kwargs):
    rts = np.random.exponential(1/abs(v), n_samples) + t
    choices = np.where(np.random.random(n_samples) < z, 1, -1)
    return {'rts': rts, 'choices': choices,
            'metadata': {'model': 'custom', 'n_samples': n_samples}}

sim = Simulator(simulator_function=my_sim, params=["v", "a", "z", "t"], nchoices=2)
results = sim.simulate(theta={'v': 0.5, 'a': 1.0, 'z': 0.5, 't': 0.3})

File ".../ssms/basic_simulators/simulator_class.py", line 675, in simulate
    x["rts"] = np.squeeze(x["rts"], axis=1)
numpy.exceptions.AxisError: axis 1 is out of bounds for array of dimension 1

Returning (n_samples, 1) arrays instead works.

Possible fixes

Either update the docstring to require (n_samples, 1), or promote 1-D returns
to 2-D in simulate() before the squeeze.

Also note the same call emits three warnings about my_sim missing max_t,
delta_t and random_state — but the docstring example only declares max_t,
so following the docs guarantees warnings.

Version: ssm-simulators 0.13.2, numpy 2.4.6, Python 3.12

[linear-code]

HSSM-698