[doc-only] Add a short toolshed/README.md

[rwgk]

Clarify expectations for the toolshed/ directory as a shared home for useful, best-effort scripts that do not require production-level maintenance.

[github-actions]

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🚀 View preview at https://nvidia.github.io/cuda-python/pr-preview/pr-2102/
https://nvidia.github.io/cuda-python/pr-preview/pr-2102/cuda-core/
https://nvidia.github.io/cuda-python/pr-preview/pr-2102/cuda-bindings/
https://nvidia.github.io/cuda-python/pr-preview/pr-2102/cuda-pathfinder/
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[kiwigitops]

Nice — having an in-tree note about toolshed/'s scope is a real improvement over the implicit convention.

One question on the "do not warrant CI coverage, unit tests, or the rest of the production-code apparatus" line: is that expectation enforced anywhere today, or only intended? Looking at the existing contents (check_cython_abi.py, check_spdx.py, the build_pathfinder_* family, etc.), some of these look CI-shaped enough that a future contributor might wire one into a workflow by reflex.

Concretely:

• Is toolshed/ excluded from the test discovery patterns (e.g. pyproject.toml pytest config, ruff/mypy include rules) so a stray test_-prefixed scratch file doesn't accidentally become CI surface?
• Would it be worth a short bullet in this README spelling out the boundary — e.g. "Files here are excluded from pytest collection and ruff/mypy checks; if a tool graduates past scratchpad status, move it to <canonical-location> first"?

Happy either way — just thinking about how a future reader who only sees this README knows where the guardrails actually live. Not blocking for a doc-only PR.