refactor(hello): enable isolated declarations (#1198)

.changeset/bumpy-birds-act.md

@@ -0,0 +1,5 @@
+---
+'@hono/hello': patch
+---
+
+Add explicit `MiddlewareHandler` return type

packages/hello/src/index.ts

@@ -1,6 +1,7 @@
+import type { MiddlewareHandler } from 'hono'
 import { createMiddleware } from 'hono/factory'
 
-export const hello = (message: string = 'Hello!') => {
+export const hello = (message: string = 'Hello!'): MiddlewareHandler => {
   return createMiddleware(async (c, next) => {
     await next()
     c.res.headers.append('X-Message', message)

packages/hello/tsconfig.build.json

@@ -4,7 +4,8 @@
     "rootDir": "src",
     "outDir": "dist",
     "tsBuildInfoFile": "dist/tsconfig.build.tsbuildinfo",
-    "emitDeclarationOnly": false
+    "emitDeclarationOnly": false,
+    "isolatedDeclarations": true
   },
   "include": ["src/**/*.ts"],
   "exclude": ["**/*.test.ts"],