⚡ Bolt: Fix parallel scanning serialization bottleneck

[acebytes]

💡 What: Changed NodeModulesScanner and CacheScanner from actor to struct to enable true parallel scanning.

🎯 Why: In Swift structured concurrency, using withTaskGroup inside an actor and calling its own methods (like findNodeModules) forces all child tasks onto the actor's single executor. This inadvertently serialized the blocking I/O operations (FileManager.default), completely preventing parallel execution. Since neither type has mutable state, converting them to structs solves this.

📊 Impact: Significantly speeds up scanning (especially node_modules scanning on large file trees) by allowing tasks to truly run concurrently across the cooperative thread pool.

🔬 Measurement: Run a scan over a large directory with many node_modules. Observe CPU core utilization (should be multithreaded) and overall wall-clock completion time.

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PR created automatically by Jules for task 2700170780368979529 started by @acebytes

[google-labs-jules]

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[acebytes]

Closing as superseded by merged #216 (NodeModulesScanner static/nonisolated refactor) + #206 (CacheScanner.scanCategory/directorySize marked nonisolated). The TaskGroup serialization bottleneck for both scanners is now resolved with the surgical nonisolated approach instead of converting actors to structs (CacheCleaner stays an actor since it isn't run in a TaskGroup).

[google-labs-jules]

Closing as superseded by merged #216 (NodeModulesScanner static/nonisolated refactor) + #206 (CacheScanner.scanCategory/directorySize marked nonisolated). The TaskGroup serialization bottleneck for both scanners is now resolved with the surgical nonisolated approach instead of converting actors to structs (CacheCleaner stays an actor since it isn't run in a TaskGroup).

Understood. Acknowledging that this work is now obsolete and superseded by the nonisolated refactors in #216 and #206. Stopping work on this task.