Add tests and implement boundary smoothing and cutout functionality

- Introduced tests for boundary smoothing in `test_boundary_smoothing.py`, verifying that smoothing reduces stair-step artifacts while preserving boundary integrity.
- Added tests for cutout boundary behavior in `test_cutout_boundary.py`, ensuring proper handling of boundary triangles and normal blending.
- Created `test_temporary_attributes.py` to check the cleanup of temporary attributes across depth modifier branches, ensuring no warnings are raised.
- Implemented point culling functionality in `test_validity.py`, confirming that invalid points are removed without affecting adjacent geometry.
- Developed boundary smoothing logic in `boundary_smoothing.py`, allowing for depth smoothing while maintaining edge integrity.
- Added cutout boundary management in `cutout_boundary.py`, including functions for removing boundary triangles and tapering thickness profiles.
- Implemented validity checks in `validity.py` to ensure proper deletion of invalid vertices and associated wire edges.

tests/tools/nodes/test_validity.py

@@ -0,0 +1,40 @@
+"""Verify point culling removes its dangling wire geometry."""
+
+import bpy
+
+from tools.nodes.common.nodes import interface_socket
+from tools.nodes.common.validity import delete_invalid_points
+
+
+def test_point_culling_removes_wire_edges_without_removing_adjacent_surface():
+    bpy.ops.wm.read_factory_settings(use_empty=True)
+    mesh = bpy.data.meshes.new("Two Quads")
+    mesh.from_pydata([(0, 0, 0), (1, 0, 0), (2, 0, 0),
+                      (0, 1, 0), (1, 1, 0), (2, 1, 0)], [],
+                     [(0, 1, 4, 3), (1, 2, 5, 4)])
+    obj = bpy.data.objects.new("Surface", mesh)
+    bpy.context.collection.objects.link(obj)
+    group = bpy.data.node_groups.new("Point Culling", "GeometryNodeTree")
+    interface_socket(group, "Geometry", "INPUT", "NodeSocketGeometry")
+    interface_socket(group, "Geometry", "OUTPUT", "NodeSocketGeometry")
+    inlet = group.nodes.new("NodeGroupInput")
+    outlet = group.nodes.new("NodeGroupOutput")
+    index = group.nodes.new("GeometryNodeInputIndex")
+    invalid = group.nodes.new("ShaderNodeMath")
+    invalid.operation = "LESS_THAN"
+    invalid.inputs[1].default_value = 1
+    group.links.new(index.outputs[0], invalid.inputs[0])
+    geometry = delete_invalid_points(group, inlet.outputs["Geometry"], invalid.outputs[0])
+    group.links.new(geometry, outlet.inputs["Geometry"])
+    modifier = obj.modifiers.new("Cull", "NODES")
+    modifier.node_group = group
+    evaluated = obj.evaluated_get(bpy.context.evaluated_depsgraph_get())
+    result = evaluated.to_mesh()
+    try:
+        assert len(result.polygons) == 1
+        assert len(result.edges) == 4
+        assert {tuple(vertex.co) for vertex in result.vertices} == {
+            (1, 0, 0), (2, 0, 0), (1, 1, 0), (2, 1, 0),
+        }
+    finally:
+        evaluated.to_mesh_clear()