Make controller Async

This PR has a large blast radius because it takes the final step and bumps up the Controller to be fully async.

We have historically done a piece-by-piece update, so all operations were already async but the controller interface was kept synchronous.

With this update, the controller is now fully async and all tests are updated.

Most places where the new C# compiler warns about function names not ending in `Async` were also adressed, giving a massive refactor change.

Functionally, no changes are done.

Tools/RemoteSynchronization/Program.cs

@@ -34,7 +34,7 @@ namespace RemoteSynchronization
         /// </summary>
         /// <param name="args">The commandline arguments.</param>
         /// <returns>0 on success, -1 on abort, and the number of errors encountered otherwise.</returns>
-        public static Task<int> Main(string[] args)
+        public static Task<int> MainAsync(string[] args)
             => RemoteSynchronizationRunner.RunAsync(args);
     }
 }