test: Add comprehensive multi-material test coverage

Add new multi-material test fixtures and 18 comprehensive test cases
to verify proper parsing of files with multiple filament types used
simultaneously. Tests cover both .gcode and .3mf formats.

New fixtures:
- OrcaFF_PLA_and_SILK.gcode (3.1 MB)
- OrcaFF_PLA_and_SILK.gcode.3mf (842 KB)

Test coverage includes:
- Parsing both .gcode and .3mf multi-material files (2x9 tests)
- Verifying individual filament properties (type, color, usage)
- Validating unit conversion (mm to meters)
- Checking consistency between file and threeMf data structures
- Confirming correct detection of all used materials

Author: GhostTypes

.claude/settings.local.json

@@ -2,7 +2,8 @@
   "permissions": {
     "allow": [
       "Bash(npx ts-node:*)",
-      "Bash(npm test)"
+      "Bash(npm test)",
+      "mcp__desktop-notifications__send-notification"
     ],
     "deny": [],
     "ask": []