Two additions to the pyplot command (E-94/95): set pyplot_subplots=N lays
the traces out as stacked subplots sharing the x-axis (N traces per panel;
0/unset = one axis), and set pyplot_style=<name> applies a matplotlib style
sheet (dark aliases dark_background). vs still means the x-axis vector
(ngspice semantics), so multi-panel is chosen with pyplot_subplots, not vs.
The verify renders a multi-RC transient with pyplot_subplots=1 (three stacked
panels), pyplot_subplots=2 (two panels for four traces), the default single
axis, and pyplot_style=dark; it checks the generated scripts for the right
plt.subplots(n, 1, …) / plt.style.use('dark_background') and that each
renders a valid PNG. Requires matplotlib. Run: python3 verify_pyplotpanel.py
(5 checks).