powerspectrum: add option to downsample raw data

lumicks/pylake/force_calibration/power_spectrum.py

@@ -454,6 +454,19 @@ def with_spectrum(self, power, num_points_per_block=1, variance=None) -> "PowerS
             variance=variance,
         )
 
+    def compress(self):
+        """Returns a compressed power spectrum by downsampling the internal data"""
+        return PowerSpectrum(
+            self.frequency,
+            self.power,
+            self.sample_rate,
+            self.total_duration,
+            self.unit,
+            num_points_per_block=self.num_points_per_block,
+            total_samples_used=self.total_samples_used,
+            variance=self._variance,
+        )
+
     def plot(self, *, show_excluded=False, **kwargs):
         """Plot power spectrum