- Updated `custom_tool_changes` function to use filament IDs instead of extruder IDs, ensuring better compatibility with mixed filament configurations.
- Enhanced `MixedFilament` structure to include a `stable_id` for persistent identity across mixed filament entries, improving remapping during updates.
- Introduced new methods for stable ID allocation and normalization in `MixedFilamentManager`.
- Updated serialization and loading functions to maintain stable IDs, ensuring consistent behavior when mixed filament entries are modified.
- Added tests to verify the correct handling of tool changes and stable ID remapping in mixed filament scenarios.
