Refactor tests and remove unused imports

- Cleaned up test files by removing unnecessary imports and unused parameters.
- Simplified test functions by eliminating redundant parameterization and consolidating logic.
- Updated test cases to directly use defined values instead of parameterized inputs where applicable.
- Enhanced readability and maintainability of the test code across various test files.

tests/support/materials.py

@@ -1,17 +1,11 @@
 import bpy
 import pytest
-from tests.support.paths import PROJECT_ROOT
 from tools.nodes.groups.image_layer import build_image_layer_group
 
 
 @pytest.fixture
-def image_layer(request):
+def image_layer():
     bpy.ops.wm.read_factory_settings(use_empty=True)
-    if getattr(request, "param", "definition") == "asset":
-        with bpy.data.libraries.load(str(PROJECT_ROOT / "src/anyimage/assets/O_AnyImage.blend")) as (_, target):
-            target.node_groups = ["O Image Layer"]
-        group = target.node_groups[0]
-    else:
-        group = build_image_layer_group()
+    group = build_image_layer_group()
     yield group
     bpy.ops.wm.read_factory_settings(use_empty=True)