Flag wasi:cli/run#run as an async function

I think this was lost in various translations here and there, but I'm under the impression that the intention is that this is should be `async`-by-default.

Author: alexcrichton

wit-0.3.0-draft/run.wit

@@ -2,5 +2,5 @@
 interface run {
   /// Run the program.
   @since(version = 0.3.0-rc-2025-08-15)
-  run: func() -> result;
+  run: async func() -> result;
 }