Use defusedxml in test files for Bandit compliance

Replace xml.etree.ElementTree with defusedxml in test files to satisfy
Bandit B314 scanner. While test XML is trusted, using defusedxml
consistently across the codebase prevents CI failures.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/tests/unit/services/test_archive_service.py

@@ -221,7 +221,7 @@ class TestPrintableObjectsExtraction:
 
     def test_extract_printable_objects_from_slice_info(self):
         """Test parsing printable objects from slice_info.config XML."""
-        from xml.etree import ElementTree as ET
+        from defusedxml import ElementTree as ET
 
         # Example slice_info.config content with 4 objects
         slice_info_xml = """<?xml version="1.0" encoding="UTF-8"?>
@@ -250,7 +250,7 @@ class TestPrintableObjectsExtraction:
 
     def test_extract_printable_objects_empty_plate(self):
         """Test handling plate with no objects."""
-        from xml.etree import ElementTree as ET
+        from defusedxml import ElementTree as ET
 
         slice_info_xml = """<?xml version="1.0" encoding="UTF-8"?>
         <config>
@@ -272,7 +272,7 @@ class TestPrintableObjectsExtraction:
 
     def test_extract_printable_objects_all_skipped(self):
         """Test handling plate where all objects are skipped."""
-        from xml.etree import ElementTree as ET
+        from defusedxml import ElementTree as ET
 
         slice_info_xml = """<?xml version="1.0" encoding="UTF-8"?>
         <config>
@@ -299,7 +299,7 @@ class TestThreeMFPlateIndexExtraction:
 
     def test_extract_plate_index_from_slice_info(self):
         """Test parsing plate index from slice_info.config metadata."""
-        from xml.etree import ElementTree as ET
+        from defusedxml import ElementTree as ET
 
         # Single-plate export from plate 5 of a multi-plate project
         slice_info_xml = """<?xml version="1.0" encoding="UTF-8"?>
@@ -325,7 +325,7 @@ class TestThreeMFPlateIndexExtraction:
 
     def test_extract_plate_index_plate_1(self):
         """Test parsing plate index when it's plate 1."""
-        from xml.etree import ElementTree as ET
+        from defusedxml import ElementTree as ET
 
         slice_info_xml = """<?xml version="1.0" encoding="UTF-8"?>
         <config>
@@ -402,7 +402,7 @@ class TestThreeMFPlateIndexExtraction:
 
     def test_high_plate_number_extraction(self):
         """Test extracting high plate numbers (e.g., plate 28)."""
-        from xml.etree import ElementTree as ET
+        from defusedxml import ElementTree as ET
 
         slice_info_xml = """<?xml version="1.0" encoding="UTF-8"?>
         <config>
@@ -433,7 +433,7 @@ class TestMultiPlate3MFParsing:
 
     def test_parse_multiple_plates_from_slice_info(self):
         """Test parsing multiple plates from slice_info.config."""
-        from xml.etree import ElementTree as ET
+        from defusedxml import ElementTree as ET
 
         # Multi-plate 3MF with 3 plates
         slice_info_xml = """<?xml version="1.0" encoding="UTF-8"?>
@@ -510,7 +510,7 @@ class TestMultiPlate3MFParsing:
 
     def test_filter_filaments_by_plate_id(self):
         """Test filtering filaments for a specific plate."""
-        from xml.etree import ElementTree as ET
+        from defusedxml import ElementTree as ET
 
         slice_info_xml = """<?xml version="1.0" encoding="UTF-8"?>
         <config>

backend/tests/unit/test_plate_object_extraction.py

@@ -1,8 +1,7 @@
 """Unit tests for plate object extraction from 3MF model_settings.config."""
 
-from xml.etree import ElementTree as ET
-
 import pytest
+from defusedxml import ElementTree as ET
 
 
 class TestPlateObjectExtraction: