feat: a function to generate URI before every connecting

**Description**

I want to add the user authentication token as query param to URI, but the token has short lifetime, while trying reconnect after token expires, there is no way to update the token, it will stuck looping.

```dart
WebSocket(
uri: () => "wss://localhost/?_token=xxxxx", // we can use the callback to retrieve valid token before connects.
);
```

**Requirements**

- [ ] A function to generate URI before every connect happens.

**Additional Context**

No.