⚡ Bolt: Batch fs operations in ArtifactStore.gc

[google-labs-jules]

💡 What: Optimized file stat and removal operations in ArtifactStore.gc to use batched concurrent operations via Promise.all with a chunk size of 10.
🎯 Why: Iterating sequentially over potentially thousands of artifact files for stats and deletions is slow. Batching these operations significantly speeds up garbage collection while avoiding OS-level EMFILE limits. Sequential state update logic is preserved prior to bulk removal to prevent race conditions.
📊 Impact: Considerably faster artifact garbage collection, particularly when cleaning up many files, reducing blocking operations.
🔬 Measurement: Verified by running unit tests for ArtifactStore and checking overall GC behavior.

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PR created automatically by Jules for task 4568542391356590326 started by @YoungSx

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