Refactor _prepare_checkpoint_paths() to return a tuple instead of having
side effects on instance variables. This prevents extra unet paths from
being incorrectly classified as checkpoints when processing extra paths.
- Changed return type from List[str] to Tuple[List[str], List[str], List[str]]
(all_paths, checkpoint_roots, unet_roots)
- Updated _init_checkpoint_paths() and _apply_library_paths() callers
- Fixed extra paths processing to properly isolate main and extra roots
- Updated test_checkpoint_path_overlap.py tests for new API
This ensures models in extra unet paths are correctly identified as
diffusion_model type and don't appear in checkpoints list.
When checkpoints and unet folders point to the same physical location
(via symlinks), prioritize checkpoints for backward compatibility.
This prevents the 'Failed to load Checkpoint root' error that users
experience when they have incorrectly configured their ComfyUI paths.
Changes:
- Detect overlapping real paths between checkpoints and unet
- Log warning to inform users of the configuration issue
- Remove overlapping paths from unet_map, keeping checkpoints
Fixes #<issue-number>
