feat: add CompositeAsyncHandler to support multiple handlers

test/util/StaticAsyncHandler.ts

@@ -0,0 +1,24 @@
+import { AsyncHandler } from '../../src/util/AsyncHandler';
+
+export class StaticAsyncHandler<TOut> extends AsyncHandler<any, TOut> {
+  private readonly canHandleStatic: boolean;
+
+  private readonly handleStatic: TOut;
+
+  public constructor (canHandleStatic: boolean, handleStatic: TOut) {
+    super();
+    this.canHandleStatic = canHandleStatic;
+    this.handleStatic = handleStatic;
+  }
+
+  public async canHandle (): Promise<void> {
+    if (this.canHandleStatic) {
+      return;
+    }
+    throw new Error('Not supported.');
+  }
+
+  public async handle (): Promise<TOut> {
+    return this.handleStatic;
+  }
+}