Supporting routes with layout and different props was broken

[SuslegStyle]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the regression has not already been reported

Last working version

2.2.0-beta.2

Stopped working in version

2.2.3

Node.js version

14.18.1

Operating system

Windows

Operating system version (i.e. 20.04, 11.3, 10)

Windows 10

💥 Regression Report

Hi There.

My test example is placed here (https://github.com/SuslegStyle/fastify-vite-hello-world)
Let me describe my use case.

I have a custom routes.js file where I define routes like

export default () => [
    {
        path: '/',
        component: Layout,
        props: {testProperty: 'Hello world'},
        children: [
            {
                path: '',
                component: Index,

            }
        ]
    },
    {
        path: '/',
        component: Layout,
        props: {testProperty: 'Hello external world'},
        children: [
            {
                path: 'external/',
                component: Index //TODO: in real app it is another page component
            }
        ]
    }
];

I use props to pass correct value to layout. In the real app, the props value changes Header.
After upgrading to 2.2.3 I start getting error during the build
Method 'GET' already declared for route '/' with constraints '{}'

Steps to Reproduce

First issue

1. Clone my example
2. Run npm run build

internal/process/promises.js:213
        triggerUncaughtException(err, true /* fromPromise */);
        ^

AssertionError [ERR_ASSERTION]: Method 'GET' already declared for route '/' with constraints '{}'
    at Router._insert (D:\fastify-vite-hello-world\node_modules\find-my-way\index.js:303:7)
    at Router._on (D:\fastify-vite-hello-world\node_modules\find-my-way\index.js:231:8)
    at Router.on (D:\fastify-vite-hello-world\node_modules\find-my-way\index.js:100:8)
    at Object.afterRouteAdded (D:\fastify-vite-hello-world\node_modules\fastify\lib\route.js:254:16)
    at D:\fastify-vite-hello-world\node_modules\fastify\lib\route.js:181:25
    at Object._encapsulateThreeParam (D:\fastify-vite-hello-world\node_modules\avvio\boot.js:551:7)
    at Boot.timeoutCall (D:\fastify-vite-hello-world\node_modules\avvio\boot.js:447:5)
    at Boot.callWithCbOrNextTick (D:\fastify-vite-hello-world\node_modules\avvio\boot.js:428:19)
    at Boot._after (D:\fastify-vite-hello-world\node_modules\avvio\boot.js:273:26)
    at Plugin.exec (D:\fastify-vite-hello-world\node_modules\avvio\plugin.js:132:19) {
  generatedMessage: false,
  code: 'ERR_ASSERTION',
  actual: false,
  expected: true,
  operator: '=='
}

Second issue

There is a second issue, that start reproducing again.
If in my routes.js change line 18 to path: '/my', then we get the error

D:\fastify-vite-hello-world\node_modules\fastify-vite\build.js:25
  const outDir = vite.build.outDir || 'dist'
                      ^

TypeError: Cannot read property 'build' of null
    at build (D:\fastify-vite-hello-world\node_modules\fastify-vite\build.js:25:23)
    at Object.fastify.vite.ready (D:\fastify-vite-hello-world\node_modules\fastify-vite\index.js:208:13)
    at processTicksAndRejections (internal/process/task_queues.js:95:5)
    at async main (D:\fastify-vite-hello-world\server.js:30:5)

Third issue

I tried to change fastify-vite/build.js file at line 25
from const outDir = vite.build.outDir || 'dist'
to const outDir = vite?.build?.outDir || 'dist'

Then the application is built successfully, but I got the runtime error that appContext is null. (We already faced the issue before)

TypeError: Cannot read property 'appContext' of null
    at useGlobalProperties (/node_modules/fastify-vite-vue/client.mjs?v=e94165ef:133:30)
    at Module.useHydration (/node_modules/fastify-vite-vue/client.mjs?v=e94165ef:20:23)
    at setup (d:/fastify-vite-hello-world/pages/index.vue:8:24)
    at _sfc_main.setup (/pages/index.vue:48:23)
    at callWithErrorHandling (D:\fastify-vite-hello-world\node_modules\vue\node_modules\@vue\runtime-core\dist\runtime-core.cjs.js:6620:22)
    at setupStatefulComponent (D:\fastify-vite-hello-world\node_modules\vue\node_modules\@vue\runtime-core\dist\runtime-core.cjs.js:6246:29)
    at setupComponent (D:\fastify-vite-hello-world\node_modules\vue\node_modules\@vue\runtime-core\dist\runtime-core.cjs.js:6202:11)
    at renderComponentVNode (D:\fastify-vite-hello-world\node_modules\vue\node_modules\@vue\server-renderer\dist\server-renderer.cjs.js:198:17)
    at renderVNode (D:\fastify-vite-hello-world\node_modules\vue\node_modules\@vue\server-renderer\dist\server-renderer.cjs.js:304:22)
    at renderVNode (D:\fastify-vite-hello-world\node_modules\vue\node_modules\@vue\server-renderer\dist\server-renderer.cjs.js:310:17)

Expected Behavior

The application should be successfully built and works properly.