drift_time_mean consistency definition

[ftoschi]

In core/s2.py, the definition of drift_mean_time includes the drift_time_gate, but it is used to evaluate parameters like the diffusion, where the gate transit time should be neglected as in this conditions the electric field is very different and the diffusion constant is very different. In #235, the drift_mean_time in s2_pattern_map_diffuse does not include the transit time by the gate:

WFSim/wfsim/core/s2.py

Line 397 in c1295aa

drift_time_mean = - z / drift_velocity_liquid

Even though the effect should be overall small, wouldn't it be better to use the drift time without the gate transit to evaluate the diffusion parameters and then add the final gate transit time in order to evaluate the time difference between S1 and S2?