perf: PNG compress_level 6 instead of optimize/9 (faster pack, ~same size on black-bg pieces)

perf: O(pieces*H*W) -> Theta(H*W) piece extraction via find_objects (103x at 190 pieces)

Pin Python 3.10 so pinned wheels (PyMuPDF/numpy/scipy) install without source builds

Deploy Dataset-Maker: torn-page non-overlapping dataset generator

initial commit