Fix checkpoint loading IsADirectoryError

[wang-h]

Bug Fix

This PR fixes #5 and #6 - the IsADirectoryError when loading pretrained encoders.

Problem

When checkpoint_filename in the config points to a directory (e.g., point_encoder), the code fails with:

Solution

Added two helper functions:

1. resolve_checkpoint_path(path) - Smart path resolver:

   • If path is a file → return as-is
   • If path is a directory → search for *.pkl, *.pt, *.pth files
   • Returns None if not found

2. get_save_path(path, default_filename) - Smart save path handler:

   • If path is a directory → append default filename
   • Ensures parent directories exist

Changes

• Improved error messages when checkpoints not found
• Auto-detection of model files in checkpoint directories
• Backward compatible with existing file paths

Testing

• Test loading from directory containing .pkl file
• Test loading from explicit file path (backward compat)
• Test saving to directory path
• Test saving to explicit file path