`prop_cycler` was made internal

[syoh]

Following code from symbulate paper errors out:

from symbulate import *

P = PoissonProcessProbabilitySpace(rate=1)
N = RV(P)
n = N.sim(100)
n.plot()
n.mean().plot()

Following is the error message:

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In[1], line 6
      4 N = RV(P)
      5 n = N.sim(100)
----> 6 n.plot()
      7 n.mean().plot()

File /opt/conda/lib/python3.11/site-packages/symbulate/results.py:608, in RVResults.plot(self, type, alpha, normalize, jitter, bins, **kwargs)
    606     alpha = np.log(2) / np.log(len(self) + 1)
    607 ax = plt.gca()
--> 608 color = get_next_color(ax)
    609 for result in self.results:
    610     result.plot(alpha=alpha, color=color, **kwargs)

File /opt/conda/lib/python3.11/site-packages/symbulate/plot.py:20, in get_next_color(axes)
     19 def get_next_color(axes):
---> 20     color_cycle = axes._get_lines.prop_cycler
     21     color = next(color_cycle)["color"]
     22     return color

AttributeError: '_process_plot_var_args' object has no attribute 'prop_cycler'

prop_cycler is from this line:

symbulate/symbulate/plot.py

Line 20 in 3ec60a1

color_cycle = axes._get_lines.prop_cycler

It seems the method prop_cycler was made internal with matplotlib 3.8: matplotlib/matplotlib#26831
(I am running matplotlib 3.8.4.)