chore: add executed outputs to split comparison notebook

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

docs: simplify spectral and bandlimited READMEs for public release

Remove internal implementation details, debugging comparison tables,
and development notes. Keep only user-facing API docs, quick start
examples, and method selection guidance.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

chore: gitignore macos files

fix(cucim): add GPU io module to match skimage.io