FIX: Use lazy import for billboard to avoid module/function name collision

Author: m-agour

fury/actor/curved.py

@@ -86,7 +86,6 @@ def sphere(
         The thickness of the wireframe lines.
     impostor : bool, optional
         Render spheres as billboard impostors instead of geometry when ``True``.
-        Defaults to ``False``.
 
     Returns
     -------
@@ -134,7 +133,7 @@ def sphere(
         obj.billboard_radii = radii_arr.copy()
         return obj
 
-    scales = radii
+    scales = radii_arr
     directions = (1, 0, 0)
 
     vertices, faces = fp.prim_sphere(phi=phi, theta=theta)
@@ -152,8 +151,6 @@ def sphere(
         wireframe=wireframe,
         wireframe_thickness=wireframe_thickness,
     )
-    obj.billboard_radii = radii_arr.copy()
-    obj.billboard_mode = "mesh"
     return obj