Prepare system extension support

Library/Network/Extension+RunBlocking.swift

@@ -0,0 +1,23 @@
+import Foundation
+import Libbox
+import NetworkExtension
+
+func runBlocking<T>(_ body: @escaping () async throws -> T) throws -> T {
+    let semaphore = DispatchSemaphore(value: 0)
+    let box = resultBox<T>()
+    Task {
+        do {
+            let value = try await body()
+            box.result = .success(value)
+        } catch {
+            box.result = .failure(error)
+        }
+        semaphore.signal()
+    }
+    semaphore.wait()
+    return try box.result.get()
+}
+
+private class resultBox<T> {
+    var result: Result<T, Error>!
+}