Optimize Cutout Geometry Nodes

- Refactor Depth Cutout to reuse the projected outline field, reducing redundant boundary calculations and improving performance.
- Derive the center field from shared low-frequency fields, eliminating an unnecessary blur operation.
- Implement triangle-only strip cleanup for Depth Cutout, as the input is confirmed to be triangulated.
- Short-circuit zero-thickness branches in both Cutout and Depth Cutout to avoid unnecessary geometry generation.
- Standardize internal attribute naming with a new `_o_` prefix and implement wildcard cleanup for temporary attributes.
- Update relevant tests to ensure functionality remains consistent and validate changes against existing behavior.

tests/tools/nodes/test_boundary_smoothing.py

@@ -170,7 +170,7 @@ def test_smoothing_without_split_moves_outline_only_within_boundary_band():
 def test_smoothed_cut_shells_stay_closed_and_separate(mode):
     from anyimage.common.object import modifier_input_identifier, set_modifier_input
 
-    obj, set_value = diagonal_surface()
+    obj, set_value = diagonal_surface(triangles=True)
     obj.data.attributes.new("o_balloon", "FLOAT", "POINT").data.foreach_set(
         "value", np.full(len(obj.data.vertices), 0.3, dtype=np.float32)
     )