Implement the '_shift' function in the prts/interfaces/time_series_metrics.py

[nocotan]

Summary

Implement the common function _shift as follows:

   def _shift(self, arr, num, fill_value=np.nan):
        arr = np.roll(arr, num)
        if num < 0:
            arr[num:] = fill_value
        elif num > 0:
            arr[:num] = fill_value
        return arr

Goal

Describe the definition by which this issue will be closed.

Todo

• [ ] Implement the common function InterfaceTimeSeriesMetrics._shift()
• [ ] Check if the unit tests are passed

Deadline

yyyy / mm / dd

Parent issue

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