[qorud02]

Fixes #139.

Add a cookbook example that uses the existing record.stage_cachers API to reuse one independent cached output when another output is missing. The recipe first recommends separate stages when that is simpler and explains that the reused value must remain valid for the current record.

Keep the executable example in examples/partial_stage_cache.py and include it directly in the documentation. Tests use the real stage decorator and file cachers: delete the second output, verify the first computation is reused, then check the case where both outputs are missing and a subsequent complete cache hit.

Validation on Windows/Python 3.14:

• Both new recipe cases pass.
• Black, isort, flake8, and git diff --check pass for the changed Python files.
• The new recipe section builds with Sphinx -W; this is a section build, not the full documentation site.
• The repository-wide suite was not run for this documentation change.

This contribution was developed with AI assistance and checked by executing the documented workflow against the actual stage and cache implementations.