🛡️ Sentinel: Fix syntax error and replace Buffer.allocUnsafe with Buffer.alloc in PersistenceLayer

[ightevenmckane187]

Fixed syntax errors and uninitialized heap memory hazards in src/os/persistence/PersistenceLayer.ts. Specifically, replaced Buffer.allocUnsafe with safe zero-filled Buffer.alloc to prevent potential memory disclosure vulnerabilities, corrected crypto.createHmac invocation syntax, and cleaned up unused buffer allocations. All TypeScript and Python test suites pass cleanly.

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PR created automatically by Jules for task 13842789731279144260 started by @ightevenmckane187

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