[Durable Objects] Deploy a Svelte site example required for Durable Objects

### Which Cloudflare product(s) does this pertain to?

Durable Objects

### Subject Matter

The way a durableobject class is exported in context of a sveltekit project.

### Content Location

https://developers.cloudflare.com/pages/framework-guides/deploy-a-svelte-site/#sveltekit-cloudflare-configuration

### Additional information

The latest create-cloudflare project generates this code in hooks.ts when you select a sveltekit project.
```
import { dev } from '$app/environment';

/*
When developing, this hook will add proxy objects to the `platform` object which
will emulate any bindings defined in `wrangler.toml`.
*/

let platform: App.Platform;

if (dev) {
const { getPlatformProxy } = await import('wrangler');
platform = await getPlatformProxy();
}

export const handle = async ({ event, resolve }) => {
if (platform) {
event.platform = {
...event.platform,
...platform
};
}

return resolve(event);
};
```

This is great. So now in `npm dev` node (using sveltekit dev mode) you can easily use KV and R2 (tested) and probably D1 bindings.

However, there is not proper example of how (or where) to export a Durable Object class.. eg:
Given this class:
```
export class DOCounter {
constructor(state: DurableObjectState, env: Env) { }
async fetch(request: Request) {
return new Response("Hello World");
}
}
```
**WHERE** do we put this class so that it forms part of the build process.
(It cannot be in a +server.ts or a +page.server.ts file. sveltekit does not like that.

Having this a `wrangler.toml` config of like this:
```
[[durable_objects.bindings]]
name = "DO_COUNTER"
class_name = "DOCounter"

migrations
[[migrations]]
tag = "v1"
new_classes = ["DOCounter"]
```

And a `/api/+server.ts` file like this:

```

export const GET: RequestHandler = async ({ request, platform }) => {
if (!platform) {
return new Response();
}
const env = platform.env;
if (!env.DO_COUNTER) {
return new Response('env.DO_COUNTER not found', { status: 404 });
}
const id = env.DO_COUNTER.idFromName(new URL(request.url).pathname);
const stub = env.DO_COUNTER.get(id);
const response = await stub.fetch(request);
return response;
};
```

PLEASE, PLEASE PLEASE create a sveltekit project that works when you do this
1. `npm run build`
2. `npx wrangler pages dev .svelte-kit/cloudflare`

To prevent this error:
```shell
Your worker has access to the following bindings:
- Durable Objects:
- DO_COUNTER: DOCounter
- KV Namespaces:
- KVCOUNTER: someKvId
- R2 Buckets:
- R2_BUCKET: r2-bucket
⎔ Starting local server...
Parsed 2 valid header rules.
✘ [ERROR] service core:user:sveltekit-cloudflare-bindings: Uncaught TypeError: Class extends value undefined is not a constructor or null

at null. (rrkgcneij6.js:18422:44) in maskDurableObjectDefinition
at null. (rrkgcneij6.js:18431:18)

✘ [ERROR] MiniflareCoreError [ERR_RUNTIME_FAILURE]: The Workers runtime failed to start. There is likely additional logging output above.
```

we are soooooo close to getting this in line. But the documentation lacks the full example that provide context of the class.

DurableObjects are easy in a simple cloudflare worker... but NOT in a sveltekit project. Does other frameworks solve this?