- Fix follow_symlinks parameter being ignored in is_dir(), is_file()
- Change from realpath() to abspath() to preserve symlinks
- Add separate caches for stat() and lstat() results
- Remove incorrect follow_symlinks param from is_symlink()
- Add comprehensive docstring explaining purpose and design
When follow_symlinks=False, methods now correctly return False for
symlinks instead of following them. Previously all symlinks were
resolved, breaking symlink-aware backup operations.
Fixes#8