Swift并发不需要import任何东西，因为它是为你导入的。
但是没有withTimeout函数。你可以写一个。或许：

extension Task where Failure == Error {
    /// Run asynchronous task, but cancel it if not finished within a certain period of time.
    ///
    /// - Parameters:
    ///   - duration: The duration before the task is canceled.
    ///   - operation: The async closure to run. The code therein should support cancelation.
    /// - Throws: If canceled, will throw `CancellationError`. If the task fails, this will throw the task’s error.
    /// - Returns: This will return the value returned by the `async` closure.

    static func withTimeout(_ duration: Duration, operation: @Sendable @escaping () async throws -> Success) async rethrows -> Success {
        let operationTask = Task.detached {
            try await operation()
        }

        let cancelationTask = Task<Void, Error>.detached {
            try await Task<Never, Never>.sleep(for: duration)
            operationTask.cancel()
        }

        return try await withTaskCancellationHandler {
            defer { cancelationTask.cancel() }
            return try await operationTask.value
        } onCancel: {
            operationTask.cancel()
        }
    }
}

不用说，我用更通用的Duration替换了TimeInterval（即秒），并使其成为Task的static方法，但总体思路很简单：基本上，为提供的闭包启动一个任务，为取消另一个任务启动另一个任务，无论哪个先完成都会取消另一个任务。显然，如果withTimeout本身被取消，那么也要取消非结构化并发任务。
但不要迷失在这杂草，因为可能有许多变化的主题，一个人可能会考虑。
你可以这样称呼它：

func fetchImageData(from url: URL) async throws -> Data {
    try await Task.withTimeout(.seconds(1))  {
        try await URLSession.shared.data(from: url).0
    }
}

所有这些都已经说过了，URLSession/URLRequest都已经有了一个超时参数，所以你也可以使用它，也许：

nonisolated func fetchImageData(from url: URL) async throws -> Data {
    let request = URLRequest(url: url, timeoutInterval: 1)
    return try await URLSession.shared.data(for: request).0
}