[Bug] ASGI cookie conversion serializes an absent Domain attribute and breaks __Host- cookies

## Expected Behavior

This surfaced in [FastMCP issue #4748](https://github.com/PrefectHQ/fastmcp/issues/4748). FastMCP's OAuth consent flow emits a valid `__Host-` cookie, but when the application runs on Azure Functions, the browser receives a `Domain` attribute and rejects it.

Azure Functions should preserve the absence of `Domain` in this ASGI response:

```http
Set-Cookie: __Host-test=value; Path=/; Secure; HttpOnly; SameSite=Lax
```

`__Host-` cookies require `Secure`, `Path=/`, and no `Domain` attribute.

## Actual Behavior

The Python ASGI response path parses `Set-Cookie` into a structured cookie and serializes the missing domain as a present, empty domain. The final response contains `domain=` or surfaces the Function App hostname as its effective domain. Browsers therefore reject the `__Host-` cookie; in FastMCP this causes the consent POST's CSRF check to fail.

## Steps to Reproduce

1. Deploy the ASGI application below to Azure Functions.
2. Request its HTTP endpoint over HTTPS.
3. Inspect the final `Set-Cookie` header and the browser cookie warnings.
4. Observe that the response includes a Domain attribute and the browser rejects `__Host-test`.

## Relevant code being tried

```python
import azure.functions as func

async def asgi_app(scope, receive, send):
assert scope["type"] == "http"

await send(
{
"type": "http.response.start",
"status": 200,
"headers": [
(b"content-type", b"text/plain"),
(
b"set-cookie",
b"__Host-test=value; Path=/; Secure; HttpOnly; SameSite=Lax",
),
],
}
)
await send(
{
"type": "http.response.body",
"body": b"ok",
"more_body": False,
}
)

app = func.AsgiFunctionApp(
app=asgi_app,
http_auth_level=func.AuthLevel.ANONYMOUS,
)
```

## Relevant log output

No application error is logged. The failure appears in the response header and browser cookie warning.

## requirements.txt file

```text
azure-functions==1.24.0
```

## Where are you facing this problem?

Production Environment

## Function app name

Not publicly shareable

## Additional Information

`azure-functions-python-library` removes the raw header and parses it with `SimpleCookie`:
https://github.com/Azure/azure-functions-python-library/blob/dev/azure/functions/http.py#L113-L116

The worker then passes the empty `cookie_entity['domain']` value to `to_nullable_string`, creating a present RPC domain:
https://github.com/Azure/azure-functions-python-worker/blob/dev/workers/azure_functions_worker/bindings/datumdef.py#L232-L245

The existing end-to-end test expects an attribute-free cookie to become `foo=bar; domain=; path=`:
https://github.com/Azure/azure-functions-python-worker/blob/dev/workers/tests/unittests/test_http_functions.py#L374-L379

A targeted fix would omit the RPC domain when `cookie_entity['domain']` is empty while preserving explicit domains. A `__Host-` regression test can verify that the final response contains `Path=/; Secure` and no `Domain`.

Bắt đầu trong workers/azure_functions_worker/bindings/datumdef.py quanh các dòng 232-245, sau đó chạy các bài kiểm thử liên quan trong workers/tests/unittests/test_http_functions.py quanh các dòng 374-379. Thêm một trường hợp hồi quy cho response __Host-test được cung cấp và xác minh rằng các thuộc tính Domain bị thiếu được lược bỏ, trong khi các domain được chỉ rõ vẫn được tuần tự hóa.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.