Light simulation issue 2: Digitizing

[YifanC]

I think there is a problem in the light_sim.digitize_signal().
I think the sample_tick should be like this line, instead of this, because "signal" is already padded.
Based on the interpolation, it would shift the signal ~100 ticks (16ns). However, I also didn't see this shift...See the examples running the second event of MiniRun5_1E19_RHC.convert2h5.00666.EDEPSIM.hdf5.

_digi: sample_tick = isample * light.LIGHT_DIGIT_SAMPLE_SPACING / light.LIGHT_TICK_SIZE
_no_digi: sample_tick = isample * light.LIGHT_DIGIT_SAMPLE_SPACING / light.LIGHT_TICK_SIZE - light.LIGHT_TRIG_WINDOW[0] / light.LIGHT_TICK_SIZE + trigger_idx[itrig]

Need help here please: @mjkramer @krwood @liviocali @AWh1t3