⚡ Optimize indexing loop by batching signature additions

[xkilldash9x]

💡 What:

• Implemented AddSignatures(sigs []detection.Signature) in pkg/storage/jsondb/json_store.go to support batch insertion of signatures.
• Refactored ID generation logic into a private ensureID helper method to reduce code duplication.
• Updated internal/cli/index.go (specifically RunIndexJSON) to collect signatures in a slice and insert them in a single batch operation instead of calling AddSignature inside the loop.

🎯 Why:

• The previous implementation called AddSignature inside a loop, acquiring and releasing a sync.RWMutex for every single signature.
• This caused excessive locking overhead and potential contention in future concurrent scenarios.
• Batching the insertion reduces the number of lock acquisitions from N (number of signatures) to 1.

📊 Measured Improvement:
Benchmark results for adding 10,000 signatures:

• Baseline (Loop): ~2.37ms (2368960 ns/op)
• Optimized (Batch): ~1.12ms (1127451 ns/op)
• Speedup: ~2.1x

This change significantly improves the throughput of the indexing process by minimizing synchronization costs.

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PR created automatically by Jules for task 9245333493878548011 started by @xkilldash9x

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