⚡ Bolt: optimize PersistenceLayer.save buffer allocations

[ightevenmckane187]

⚡ Bolt: optimize PersistenceLayer.save buffer allocations

• Fixed syntax and reference issues in PersistenceLayer.save.
• Pre-allocated single output Buffer using Buffer.allocUnsafe().
• Wrote string payload directly into output Buffer with out.write().
• Updated HMAC signature directly from string payload, bypassing intermediate Buffer allocations.
• Verified all 45 test suites pass and measured benchmark performance using npx tsx benchmarks/persistence_bench.ts.

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PR created automatically by Jules for task 15508383983522467980 started by @ightevenmckane187

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