Add GitHub update checker and installer

Library/Network/HTTPClient.swift

@@ -45,7 +45,41 @@ public class HTTPClient {
         }
     }
 
+    public func writeTo(_ url: String?, path: String, progress: ((Int64, Int64) -> Void)? = nil) throws {
+        #if DEBUG
+            precondition(!Thread.isMainThread, "HTTPClient.writeTo(...) must not be called on the main thread")
+        #endif
+        let request = client.newRequest()!
+        request.setUserAgent(HTTPClient.userAgent)
+        try request.setURL(url)
+        let response = try request.execute()
+        if let progress {
+            let handler = WriteToProgressHandler(progress)
+            try response.writeTo(withProgress: path, handler: handler)
+        } else {
+            try response.write(to: path)
+        }
+    }
+
+    public static func writeToAsync(_ url: String?, path: String, progress: ((Int64, Int64) -> Void)? = nil) async throws {
+        try await BlockingIO.run {
+            try HTTPClient().writeTo(url, path: path, progress: progress)
+        }
+    }
+
     deinit {
         client.close()
     }
 }
+
+private class WriteToProgressHandler: NSObject, LibboxHTTPResponseWriteToProgressHandlerProtocol {
+    private let handler: (Int64, Int64) -> Void
+
+    init(_ handler: @escaping (Int64, Int64) -> Void) {
+        self.handler = handler
+    }
+
+    func update(_ progress: Int64, total: Int64) {
+        handler(progress, total)
+    }
+}