⚡ Bolt: Fix TaskGroup serialization bottleneck by changing actors to structs

[acebytes]

💡 What: Changed CacheScanner, NodeModulesScanner, and CacheCleaner from actors to structs.
🎯 Why: Using an actor with withTaskGroup for synchronous file system operations unintentionally serializes task execution on the actor's executor. By using structs for these stateless components, TaskGroups can distribute work across multiple threads, enabling true parallelism for I/O operations.
📊 Impact: Significantly reduces the time required for cache and node_modules scanning by processing multiple directories concurrently instead of sequentially.
🔬 Measurement: Observe CPU utilization and total scan duration before and after the change; concurrent execution should utilize more CPU cores and finish faster.

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PR created automatically by Jules for task 5947531008339055548 started by @acebytes

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