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.

tools/nodes/common/cutout_boundary.py

@@ -0,0 +1,45 @@
+"""Clean cutout boundary triangles and taper the split thickness profile."""
+
+from .depth_surface import _math
+from .nodes import evaluate_field, group_input, read_float_attribute, sample_field, store_float_attribute
+from .smoothing import edge_boundary_field
+from .boundary_smoothing import boundary_influence
+
+
+def remove_boundary_triangles(group, geometry):
+    """Remove all-boundary triangles once on the current topology."""
+    nodes, links = group.nodes, group.links
+    rim = evaluate_field(group, edge_boundary_field(nodes, links), "FLOAT", "POINT")
+    all_boundary = _math(group, "GREATER_THAN", evaluate_field(group, rim, "FLOAT", "FACE"), 0.99999)
+    count = nodes.new("GeometryNodeInputMeshFaceNeighbors").outputs["Vertex Count"]
+    selected = _math(group, "MULTIPLY", all_boundary, _math(group, "COMPARE", count, 3))
+    delete = nodes.new("GeometryNodeDeleteGeometry")
+    delete.domain, delete.mode = "FACE", "ALL"
+    links.new(geometry, delete.inputs["Geometry"])
+    links.new(selected, delete.inputs["Selection"])
+    return delete.outputs["Geometry"]
+
+
+def taper_split_profile(group, original, geometry):
+    """Taper balloon thickness through the shared two-ring influence builder."""
+    nodes, links = group.nodes, group.links
+    uv = nodes.new("GeometryNodeInputNamedAttribute")
+    uv.data_type = "FLOAT_VECTOR"
+    uv.inputs["Name"].default_value = "UVMap"
+    original_uv = nodes.new("GeometryNodeSetPosition")
+    links.new(original, original_uv.inputs["Geometry"])
+    links.new(uv.outputs["Attribute"], original_uv.inputs["Position"])
+    nearest = nodes.new("GeometryNodeSampleNearest")
+    nearest.domain = "POINT"
+    links.new(original_uv.outputs["Geometry"], nearest.inputs["Geometry"])
+    links.new(uv.outputs["Attribute"], nearest.inputs["Sample Position"])
+    rim = evaluate_field(group, edge_boundary_field(nodes, links), "FLOAT", "POINT")
+    protected = sample_field(group, original, rim, "FLOAT", index=nearest.outputs["Index"])
+    influence = boundary_influence(group, protected)
+    controls = group_input(nodes, {"Edge Round", "Split Threshold"})
+    strength = _math(group, "ADD", 1, _math(group, "MULTIPLY", controls.outputs["Edge Round"], 4))
+    band = _math(group, "MINIMUM", _math(group, "MULTIPLY", influence, strength), 1)
+    band = _math(group, "MULTIPLY", band, _math(group, "GREATER_THAN", controls.outputs["Split Threshold"], 0))
+    retained = _math(group, "SQRT", _math(group, "MAXIMUM", _math(group, "SUBTRACT", 1, band), 0))
+    profile = _math(group, "MULTIPLY", read_float_attribute(group, "o_balloon"), retained)
+    return store_float_attribute(group, geometry, "o_balloon", profile)