Add comprehensive tests for image processing nodes and refactor node imports

- Introduced new test files for image layer, image plane, normal scale, object normal rotation, shadeless, and temporary attributes.
- Implemented tests to validate the behavior of alpha curves, depth layers, and normal scales in various rendering engines.
- Refactored import paths for node groups to align with the new directory structure.
- Added checks for temporary attribute lifetimes and ensured proper cleanup without warnings.
- Enhanced CLI commands to require the Blender group and validate the presence of generated node assets before packaging.
- Updated packaging scripts to enforce the existence of necessary assets, preventing build failures.

tests/nodes/test_image_layer.py

@@ -0,0 +1,38 @@
+import numpy as np
+import pytest
+
+
+from tests.support.materials import image_layer
+from nodes.groups.image_depth_layer import build_image_depth_layer_group
+
+
+def test_alpha_curve_preserves_endpoints_and_suppresses_soft_edges(image_layer):
+    inputs = {
+        item.name: item for item in image_layer.interface.items_tree
+        if item.item_type == "SOCKET" and item.in_out == "INPUT"
+    }
+    assert list(inputs) == [
+        "Color", "Alpha", "Normal", "Normal Scale", "Bump Scale",
+        "Alpha Fix", "Object Space",
+    ]
+    output = next(node for node in image_layer.nodes if node.type == "GROUP_OUTPUT")
+    curve = output.inputs["Alpha"].links[0].from_node
+    assert curve.type == "CURVE_FLOAT"
+    assert curve.inputs["Value"].links[0].from_socket.name == "Alpha"
+    assert curve.inputs["Factor"].links[0].from_socket.name == "Alpha Fix"
+    mapping = curve.mapping
+    samples = np.array([
+        mapping.evaluate(mapping.curves[0], float(alpha))
+        for alpha in np.linspace(0, 1, 1001)
+    ])
+    np.testing.assert_allclose(samples[:801], 0, atol=3e-4)
+    assert samples[-1] == pytest.approx(1)
+
+
+def test_depth_layer_keeps_foreground_alpha_threshold(image_layer):
+    depth = build_image_depth_layer_group()
+    output = next(node for node in depth.nodes if node.type == "GROUP_OUTPUT")
+    threshold = output.inputs["Alpha"].links[0].from_node
+    assert threshold.operation == "GREATER_THAN"
+    assert threshold.inputs[1].default_value == 0.5
+    assert threshold.inputs[0].links[0].from_socket.name == "Alpha"