feat: add image scaling, duplicate detection, and atlas cropping options

[zlatkok]

• Duplicate Detection: Implement detect_duplicates to identify pixel-identical sprites and alias them in the output configuration, saving texture space.
• Image Scaling: Add scale and scale_filter options to resize input images using PIL filters (e.g., BICUBIC, NEAREST) before packing.
• Atlas Optimization: Add crop_atlas to trim the final texture to the actual content size and ignore_blank to exclude fully transparent images.
• Debugging: Add draw_border option to visualize sprite boundaries in the generated atlas.
• API Enhancements: Update pack() and multi_pack() to return atlas data and add support for post_process_routine hooks.
• Refactoring: Centralize path extraction logic in MaxRectsAtlas and update documentation for new parameters.