⚡ Bolt: Fix TaskGroup serialization in NodeModulesScanner

[acebytes]

• 💡 What: Added the nonisolated keyword to findNodeModules and directorySize in NodeModulesScanner.
• 🎯 Why: In Swift Concurrency, calling an actor-isolated method from inside a TaskGroup subtask serializes execution on the actor's executor, completely eliminating parallelism. Making these methods nonisolated ensures they run concurrently on the global pool.
• 📊 Impact: Significant reduction in scan time for node_modules by actually processing directories in parallel as originally intended.
• 🔬 Measurement: Verify scan speed using the CLI or UI; it should complete noticeably faster on systems with multiple large project directories.

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PR created automatically by Jules for task 4900282487562487202 started by @acebytes

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