correctly initialize and expose empty sequences

src/async/impl.ts

@@ -1072,7 +1072,7 @@ abstract class BaseOrderedAsyncSequence<TElement> extends BaseAsyncSequence<TEle
   }
 }
 
-export class EmptyAsyncSequence<T> extends BaseAsyncSequence<T> {
+class EmptyAsyncSequence<T> extends BaseAsyncSequence<T> {
   override async nonEnumeratedCount() {
     return 0;
   }
@@ -1080,6 +1080,8 @@ export class EmptyAsyncSequence<T> extends BaseAsyncSequence<T> {
   override async *iterator() { }
 }
 
+export const EMPTY = new EmptyAsyncSequence<any>();
+
 export class RangeAsyncSequence extends BaseAsyncSequence<number> {
   readonly #min: number;
   readonly #max: number;