Sacramento PaintBench moved into OpenCastor

This benchmark now lives inside the OpenCastor runtime as castor bench sacpaint (import name castor.bench.sacpaint). The last standalone release was sacpaint 0.3.1 on PyPI. From 0.4.0 the PyPI package sacpaint is a pointer: it contains no code and only depends on opencastor[paintbench], so pip install sacpaint still installs the benchmark (import sacpaint no longer works; use castor.bench.sacpaint). Everything lives in craigm26/OpenCastor.

pip install "opencastor[paintbench]"
castor bench sacpaint score photo-of-my-drawing.jpg
castor bench sacpaint run --policy sacpaint_trace --embodiment sacpaint_plotter --no-rerun --no-prompt

Docs: docs/benchmarks/sacpaint.md. The task names (sacpaint/photo-v1, sacpaint/line-v0), the reference hashes, the scorers and the media categories are unchanged by the move.