[ENH] Add fig.mne container for colorbar (#13019)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

doc/changes/devel/13019.newfeature.rst

@@ -0,0 +1 @@
+Add ``fig.mne`` container for :class:`Colorbar <matplotlib.colorbar.Colorbar>` in :func:`plot_connectivity_circle <mne_connectivity.viz.plot_connectivity_circle>` to allow users to access it directly, by `Santeri Ruuskanen`_.

mne/viz/circle.py

@@ -6,6 +6,7 @@
 
 from functools import partial
 from itertools import cycle
+from types import SimpleNamespace
 
 import numpy as np
 
@@ -371,6 +372,7 @@ def _plot_connectivity_circle(
         cb_yticks = plt.getp(cb.ax.axes, "yticklabels")
         cb.ax.tick_params(labelsize=fontsize_colorbar)
         plt.setp(cb_yticks, color=textcolor)
+        fig.mne = SimpleNamespace(colorbar=cb)
 
     # Add callback for interaction
     if interactive:

mne/viz/tests/test_circle.py

@@ -17,7 +17,10 @@ def test_plot_channel_labels_circle():
     fig, axes = plot_channel_labels_circle(
         dict(brain=["big", "great", "smart"]),
         colors=dict(big="r", great="y", smart="b"),
+        colorbar=True,
     )
+    # check that colorbar handle is returned
+    assert isinstance(fig.mne.colorbar, matplotlib.colorbar.Colorbar)
     texts = [
         child.get_text()
         for child in axes.get_children()