fix: should export Application (#6)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Refactor**
- Updated import and export declarations for the `Application` class to
improve code clarity and maintainability.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

src/application.ts

@@ -28,7 +28,7 @@ export type { ContextDelegation as Context } from './context.js';
  * Expose `Application` class.
  * Inherits from `Emitter.prototype`.
  */
-export default class Application extends Emitter {
+export class Application extends Emitter {
   /**
    * Make HttpError available to consumers of the library so that consumers don't
    * have a direct dependency upon `http-errors`
@@ -274,3 +274,5 @@ export default class Application extends Emitter {
     res.end(body);
   }
 }
+
+export default Application;

src/index.ts

@@ -1,4 +1,4 @@
-import Application from './application.js';
+import { Application } from './application.js';
 
 export default Application;
 

test/application/context.test.ts

@@ -1,11 +1,11 @@
 import assert from 'node:assert';
 import request from 'supertest';
-import Koa from '../../src/index.js';
+import { Application } from '../../src/index.js';
 
 describe('app.context', () => {
-  const app1 = new Koa();
+  const app1 = new Application();
   app1.context.msg = 'hello app1';
-  const app2 = new Koa();
+  const app2 = new Application();
   app2.request.foo = 'bar';
 
   it('should the context between apps is isolated', () => {