Explain Swift's concurrency model with async/await and actors.

Swift's modern concurrency model provides structured concurrency with async/await and actors for safe concurrent programming.\n\n• **Async/Await:**\n• Eliminates callback hell and completion handlers\n• Provides sequential-looking asynchronous code\n• Automatic suspension and resumption\n• Structured concurrency with task hierarchies\n\n\nfunc fetchData() async throws -> Data {\n let url = URL(string: "https://api.example.com")!\n let (data, _) = try await URLSession.shared.data(from: url)\n return data\n}\n\n// Usage\nTask {\n do {\n let data = try await fetchData()\n print("Received data: \(data)")\n } catch {\n print("Error: \(error)")\n }\n}\n\n\n• **Actors:**\n• Provide thread-safe access to mutable state\n• Isolate state and ensure serial access\n• Prevent data races at compile time\n• Support async methods and properties\n\n\nactor BankAccount {\n var balance: Double = 0\n \n func deposit(_ amount: Double) {\n balance += amount\n }\n \n func withdraw(_ amount: Double) -> Bool {\n guard balance >= amount else { return false }\n balance -= amount\n return true\n }\n}\n