Support cancelling RootCommand

mobile/src/main/java/be/mygod/librootkotlinx/RootServer.kt

@@ -420,15 +420,21 @@ class RootServer @JvmOverloads constructor(private val warnLogger: (String) -> U
                             Log.e(command.javaClass.simpleName, "Unexpected exception in RootCommandOneWay", e)
                         }
                     }
-                    is RootCommand<*> -> defaultWorker.launch {
+                    is RootCommand<*> -> {
+                        val commandJob = Job()
+                        cancellables[callback] = { commandJob.cancel() }
+                        defaultWorker.launch(commandJob) {
                             val result = try {
                                 val result = command.execute();
                                 { output.pushResult(callback, result) }
                             } catch (e: Throwable) {
                                 { output.pushThrowable(callback, e) }
+                            } finally {
+                                cancellables.remove(callback)
                             }
                             withContext(callbackWorker) { result() }
                         }
+                    }
                     is RootCommandChannel<*> -> defaultWorker.launch {
                         val result = try {
                             coroutineScope {