ci: rewrite storage policy for Blacksmith sticky disks and colocated cache

[DecisionNerd]

Summary

• Rewrite test-ci-storage-policy.py as Blacksmith-first (sticky disks, colocated actions/cache@v6, sticky SCCACHE_DIR; forbid target/ in cache blobs and maturin GHA sccache).
• Document allowed/forbidden table and expected Binding RC sticky key shapes in workflows README.
• Prefer policy/docs in this PR; Binding RC sticky mounts land in ci: cut Binding RC wall-clock with sticky disks, runners, and slim acceptance #387 / PR ci: accelerate Binding RC builds #392.

Closes #385.

Test plan

• python3 scripts/ci/test-ci-storage-policy.py
• CI Gate green

Made with Cursor

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Note

Update CI storage policy script and docs for Blacksmith sticky disks

• Expands the README.md with a new section documenting allowed and forbidden CI storage patterns, expected sticky-disk keys, and notes on PR/macOS/Windows behavior.
• Updates error messages in test-ci-storage-policy.py to give actionable guidance: the actions/cache violation now names stickydisk as the correct alternative, and the Maturin sccache:true violation now explains the GitHub-integrated backend and recommends sticky SCCACHE_DIR/target.
• No logic or detection changes — only message text and documentation are updated.

^{Macroscope summarized f286bd4.}

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📥 Commits

Reviewing files that changed from the base of the PR and between 1d8844b and f286bd4.

⛔ Files ignored due to path filters (1)

• .github/workflows/README.md is excluded by !**/*.md, !**/.github/**

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• scripts/ci/test-ci-storage-policy.py

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