[Bug] Energy has imaginary values at initial time

[kbidzhiev]

MVP

seq = make_adiabatic_afm_state_2d_seq(2, 2)


observables = [Energy(evaluation_times=[0]),]
noise_model = pulser.noise_model.NoiseModel(
    depolarizing_rate=0.2  # <-- this causing an error
 )  

config = emu_mps.MPSConfig(
    observables=observables,
    noise_model=noise_model,
)
backend = emu_mps.MPSBackend(seq, config=config)
result = backend.run()

output

  File "emulators/emu_mps/custom_callback_implementations.py", line 95, in energy_mps_impl
    assert torch.allclose(h.imag, torch.zeros_like(h.imag), atol=1e-4)
           ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^