BUG: check_coupling_params fails because of hard-coded sampling frequency

[ctrltz]

Trying to simulate 60 Hz oscillations with coupling, but the sampling frequency is set to 100 Hz in check_coupling_params:

sim.set_coupling(
    ("v1-lh", "v1-rh"), method=ppc_shifted_copy_with_noise,
    phase_lag=0, coh=1, fmin=59, fmax=61
)

As a result, filtering fails because target frequency is higher than the Nyquist one, error message:

ValueError: Digital filter critical frequencies must be 0 < Wn < 1

[ctrltz]

Temporary fix in 839c7d3: raised the sampling frequency to 500 Hz.