Async onResponse

### Prerequisites

- [X] I have written a descriptive issue title
- [X] I have searched existing issues to ensure the issue has not already been raised

### Issue

Hello!
Can someone clarify is it possible or not using async onResponse hook with `@fastify/reply-from` plugin? Sometimes with async onResponse in my logs I see error:
```
"stack":"FastifyError: Reply was already sent, did you forget to return reply
at Reply.send (/node_modules/fastify/lib/reply.js:151:26)
at /node_modules/@fastify/reply-from/index.js:205:14
at /node_modules/@fastify/reply-from/index.js:284:9
at /node_modules/@fastify/reply-from/lib/request.js:177:7
at RequestHandler.runInAsyncScope (node:async_hooks:203:9)
at RequestHandler.onHeaders (/node_modules/@fastify/reply-from/node_modules/undici/lib/api/api-request.js:104:14)
at Request.onHeaders (/node_modules/@fastify/reply-from/node_modules/undici/lib/core/request.js:275:29)
at Parser.onHeadersComplete (/node_modules/@fastify/reply-from/node_modules/undici/lib/client.js:920:27)
at wasm_on_headers_complete (/node_modules/@fastify/reply-from/node_modules/undici/lib/client.js:536:30)
at wasm://wasm/0003626a:wasm-function[11]:0x494
at wasm://wasm/0003626a:wasm-function[51]:0x1003
at wasm://wasm/0003626a:wasm-function[68]:0x6e8e
at wasm://wasm/0003626a:wasm-function[67]:0x1568
at wasm://wasm/0003626a:wasm-function[21]:0x552
at Parser.execute (/node_modules/@fastify/reply-from/node_modules/undici/lib/client.js:677:22)
at Parser.readMore (/node_modules/@fastify/reply-from/node_modules/undici/lib/client.js:646:12)","code":"FST_ERR_REP_ALREADY_SENT","name":"FastifyError","statusCode":500},"msg":"Reply was already sent, did you forget to return reply
```

My goal is changing a response body:
```ts
// Proxy to another Api
return reply.from(proxyPath, {
rewriteRequestHeaders() {
return proxyHeaders;
},
rewriteHeaders(headers) {
return createProxyHeaders(proxyUrl, headers);
},
async onResponse(_req, reply, res) {
const resBody = await new Promise((resolve, reject) => {
let buffer = Buffer.from('', 'utf8');

res.on('data', (chunk) => (buffer = Buffer.concat([buffer, chunk])));

res.on('end', async () => {
resolve(buffer.toString());
});

res.on('error', (error) => {
reject(error);
});
});

// do something with resBody

return reply.send(resBody);
}
```