🛡️ Sentinel: Fix uninitialized memory leak in PersistenceLayer

[ightevenmckane187]

🛡️ Sentinel: Fix uninitialized memory leak in PersistenceLayer.save

• Severity: HIGH / MEDIUM
• Vulnerability: Uninitialized heap memory allocation via Buffer.allocUnsafe in PersistenceLayer serialization path.
• Impact: Potential leakage of stale heap memory contents if unwritten buffer segments are read or transmitted.
• Fix: Replaced Buffer.allocUnsafe with safe Buffer.alloc and resolved stray compilation/syntax errors in PersistenceLayer.ts.
• Verification: Passed tests/persistence_security.test.ts and benchmarks/persistence_bench.ts.

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PR created automatically by Jules for task 1531390686127256028 started by @ightevenmckane187

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