[Bug] non-async call in async fn

### Checklist

- [x] 1. I have searched related issues but cannot get the expected help.
- [x] 2. The bug has not been fixed in the latest version.
- [x] 3. Please note that if the bug-related issue you submitted lacks corresponding environment info and a minimal reproducible demo, it will be challenging for us to reproduce and resolve the issue, reducing the likelihood of receiving feedback.

### Describe the bug

这个 async 是不是假的，里面的 forward 是同步的，CPU 执行到这里，等待 GPU 过程中不会让出执行权。
https://github.com/InternLM/lmdeploy/blob/main/lmdeploy/pytorch/engine/model_agent.py#L260

### Reproduction

https://github.com/InternLM/lmdeploy/blob/main/lmdeploy/pytorch/engine/model_agent.py#L260

### Environment

```Shell
https://github.com/InternLM/lmdeploy/blob/main/lmdeploy/pytorch/engine/model_agent.py#L260
```

### Error traceback

```Shell

```