Add record amplitude bit shift

[JelleAalbers]

This adds the field amplitude_bit_shift to records, as introduced by @zhut19 in XENONnT/straxen#38. This will help make desaturation corrections possible, e.g. based on pulse shape as in XENON1T or using the attenuated / high-energy channels (@ariannarocchetti @petergaemers).

Setting this field means the amplitude the data should be multiplied by 2**amplitude_bit_shift before it is used. Currently, desaturation corrections cannot store amplitudes above 2**15 -1, since strax uses signed 16-bit integers (np.int16) to represent waveforms. After this, a correction function could set amplitude_bit_shift = 1 (or 2, 3, etc) and divide the whole waveform by 2 (or 4, 8, etc), so it can store higher amplitudes while staying within the allowed integer range. Of course this loses some precision, but for a giant waveform that seems acceptable.

I went through the pulse processing / integration routines to change them were needed, but it would be great if someone could check if I did it correctly or missed some function. Even better would be to test this of course.

The baseline field is assumed to be left unaffected by the multiplier. Thus, we do not use the multiplier when correcting integrals for the non-integer part of the baseline (see #2).

This also implements Tianyu's proposed fix in #256 for the saturated channel counting. The saturation check takes into account the multiplier, so a channel will still be flagged as saturated even after a desaturation correction is run on it.