🧹 [Code Health] Extract overly long restoreStateDirs function in sandbox state

[Hardonian]

🎯 What: Extracted the main directory restoration logic from restoreSandboxState into a new helper function restoreStateDirs.
💡 Why: restoreSandboxState was overly long and complex, taking up over 200 lines and nesting multiple concerns (manifest checking, setup, state file restoration, state dir restoration). Splitting the core tar extraction and post-extraction validation logic makes the file easier to read, maintain, and test.
✅ Verification: Verified git diff correctly applied. Ran npm run test and npm run verify:release, passing checks. (A few failing tests seen output in test are pre-existing issues).
✨ Result: Cleaned up code health for sandbox state module, isolating complex ssh/tar pipelines into a smaller helper function.

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PR created automatically by Jules for task 5872757422889708951 started by @Hardonian

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