Correcting distortions via Qblox backend (#285, QAE-40)

Explanation of changes

This MR implements distortion correction as a standalone method quantify_scheduler.backends.corrections.apply_distortion_corrections. The Qblox backend calls the method before going into the actual compilation of the schedule (https://gitlab.com/quantify-os/quantify-scheduler/blob/QAE-40-correction-layer/quantify_scheduler/backends/qblox_backend.py#L59)

Overview:

• apply_distortion_corrections replaces to-be-corrected pulses in operations in the schedule by pre-sampled pulses with filter function applied to the sample, by calling quantify_scheduler.backends.corrections.distortion_correct_pulse;

• To-be-corrected pulses are identified by their port-clock combination;

• apply_distortion_corrections looks for a key "distortion_corrections" at the top level of the hardware configuration file, with the fields:

  "distortion_corrections": {
      "q0:fl-cl0.baseband": {
          "filter_func": "scipy.signal.lfilter",
          "input_var_name": "x",
          "kwargs": {
              "b": [],
              "a": 1
          },
          "clipping_values": [-2.5, 2.5]
      }
  }

Motivation of changes

The distortion correction methods are separated from the Qblox backend itself, allowing for any backend to make use of them.

Closes #285

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