Access settings dictionary-style in _PlotManager

At this point, all settings should be present and resolved.

src/python_spectrometer/core.py

@@ -370,7 +370,7 @@ class _PlotManager:
         y = self._data[key][f'timetrace_{line_type}'][-1]
         if np.iscomplexobj(y):
             y = np.abs(y)
-        x = np.arange(y.size) / self._data[key]['settings'].fs
+        x = np.arange(y.size) / self._data[key]['settings']['fs']
 
         d = self.lines[key]['time'][line_type]
         if line := d['line']:
@@ -560,7 +560,7 @@ class _PlotManager:
     def set_xlims(self):
         # Frequency-axis plots
         right = max((
-            self._data[k]['settings'].f_max
+            self._data[k]['settings']['f_max']
             + (self._data[k]['settings'].get('freq', 0)
                if self.plot_absolute_frequencies else 0)
             for k in self.shown
@@ -570,14 +570,14 @@ class _PlotManager:
                 or self.axes['main']['processed'].get_xscale() == 'log'
         ):
             left = min((
-                self._data[k]['settings'].f_min
+                self._data[k]['settings']['f_min']
                 + (self._data[k]['settings'].get('freq', 0)
                    if self.plot_absolute_frequencies else 0)
                 for k in self.shown
             ), default=None)
         else:
             left = min((
-                - self._data[k]['settings'].f_max
+                - self._data[k]['settings']['f_max']
                 + (self._data[k]['settings'].get('freq', 0)
                    if self.plot_absolute_frequencies else 0)
                 for k in self.shown
@@ -677,8 +677,8 @@ class _PlotManager:
             x += self._data[key]['settings'].get('freq', 0)
 
         window = self._data[key]['settings'].get('window', 'hann')
-        nperseg = self._data[key]['settings'].nperseg
-        fs = self._data[key]['settings'].fs
+        nperseg = self._data[key]['settings']['nperseg']
+        fs = self._data[key]['settings']['fs']
 
         y = np.mean(self._data[key][f'S_{line_type}'], axis=0)
         if not self.plot_density or dB: