⚡ Bolt: Optimize ArtifactStore GC

[google-labs-jules]

• 💡 What: Optimize ArtifactStore.gc file iteration by replacing sequential fs.stat and fs.rm calls with batched concurrent operations (chunk size 10), while preserving a sequential building process for the state-dependent file removal queue.
• 🎯 Why: Iterating sequentially over a potentially large number of artifact files creates a severe performance bottleneck and scaling issues. Using un-chunked concurrent promises can lead to EMFILE errors. Combining a sequentially-built safe queue with chunked I/O avoids race conditions for cumulative total logic (e.g. maxTotalBytes) while safely providing large performance gains for file interactions.
• 📊 Impact: Substantially speeds up garbage collection times for environments with high artifact volumes and lowers max duration constraints for periodic GC tasks.
• 🔬 Measurement: Observe GC iteration speeds when generating hundreds of artifacts; verify that GC limits maxFiles and maxTotalBytes are strictly maintained without EMFILE errors.

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PR created automatically by Jules for task 3471941373029360802 started by @YoungSx

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