Fix strict timing gaps in NV center XY8 scripts

[NicolasStaudenmaier]

The script tau sweep program for the NV center XY8 measurements 09b_xy8_tau.py will evaluate strict timing errors in the real time processing. These gaps can be bridged by introducing a fixed wait time. To keep correct timing of the XY8 sequence the same duration is subtracted from a directly following waiting time of a QUA variable.
The exact duration of this gap, however, depends on the QOP version and sequence parameters. With a waiting time of 10 clock cycles most common parameters are well covered.

In the order sweep measurement 09c_xy8_order.py an error of not converting ns to clock cycles is fixed.