Fix connected theta edges for plot3d (#1237)

Currently, if you don't give a full theta grid to `plot_3d`, it will
connect the theta edges and end up this kind of plots,

![image](https://github.com/user-attachments/assets/3b4fe4be-6bb5-45aa-922e-977401fb910a)

I don't know about you, but I want it to behave like this,

![image](https://github.com/user-attachments/assets/695994a0-1c5d-4b17-a4ff-98319fcf3888)

desc/plotting.py

@@ -971,9 +971,9 @@ def plot_3d(
     if grid.num_rho == 1:
         n1, n2 = grid.num_theta, grid.num_zeta
         if not grid.nodes[-1][2] == 2 * np.pi:
-            p1, p2 = True, False
+            p1, p2 = False, False
         else:
-            p1, p2 = True, True
+            p1, p2 = False, True
     elif grid.num_theta == 1:
         n1, n2 = grid.num_rho, grid.num_zeta
         p1, p2 = False, True