simplify asyncMap implementation (#11252)

Co-authored-by: Jerel Miller <[email protected]>

Author: phryneas

src/testing/internal/index.ts

@@ -1,2 +1,3 @@
 export * from "./profile/index.js";
 export * from "./disposables/index.js";
+export { ObservableStream } from "./ObservableStream.js";