Optional path parameter like `[[id]]` is not working

If an api route like `/api/users/[[id]]` is created, this `[[id]]` string will become `{[id}]` and it does not work in swagger.


sveltekit error
```shell
SvelteKitError: Not found: /api/mapstyle/images/%7B[id%7D]
```

- Sveltekit optional path param endpoint
https://svelte.dev/docs/kit/advanced-routing#Optional-parameters

Alternatively, I can create two +server.ts for `/api/users` and `/api/users/{id}`, but It would be nice if this package can support optional path param.

Start with the +server.ts route entry points and trace how `/api/users/[[id]]` is converted for Swagger/OpenAPI. Compare the generated `{[id}]` path with SvelteKit's optional path parameter syntax; done means the optional route works without a malformed path and is represented correctly in the API documentation.

Written by the indexing model from the issue text.