fix: export Router Class (#277)

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

## Summary by CodeRabbit

- **New Features**
- Introduced explicit export of the `Router` class from `@eggjs/router`.
- Enhanced lifecycle management with new methods in the `EggCore` class.

- **Bug Fixes**
- Updated dependency version for `@eggjs/koa`, potentially addressing
minor issues.

- **Documentation**
- Added deprecation warnings for certain methods in the `EggCore` class
to guide users on best practices.

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

package.json

@@ -35,7 +35,7 @@
   },
   "homepage": "https://github.com/eggjs/core#readme",
   "dependencies": {
-    "@eggjs/koa": "^2.20.1",
+    "@eggjs/koa": "^2.20.2",
     "@eggjs/router": "^3.0.5",
     "@eggjs/utils": "^4.0.2",
     "egg-logger": "^3.5.0",

src/egg.ts

@@ -37,6 +37,7 @@ export type EggCoreInitOptions = Partial<EggCoreOptions>;
 // export @eggjs/koa classes
 export {
   KoaRequest, KoaResponse, KoaContext, KoaApplication,
+  Router,
 };
 
 // export @eggjs/koa types