⚡ Bolt: Parallelize bulk file deletion in CacheCleaner

[acebytes]

💡 What: Refactored removeContents(of:) in CacheCleaner to execute FileManager.removeItem concurrently using withThrowingTaskGroup and a sliding window iterator.
🎯 Why: Sequential removeItem inside a loop executes synchronously, causing O(N) blocking disk I/O and potential cooperative thread pool exhaustion, leading to sluggish UI updates and slow overall cache cleanup.
📊 Impact: Expected to significantly reduce cache clearance times (up to 8x faster depending on disk capabilities and thread availability) by parallelizing file I/O operations effectively.
🔬 Measurement: Execute a permanent cache cleanup (moveToTrash: false) on a category with numerous small files and observe the reduction in time taken to free the disk space compared to the synchronous approach.

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PR created automatically by Jules for task 13216076028287996049 started by @acebytes

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