[Improve][SDK] Fix potential goroutine leak on close in the DataProxy Go SDK by closing connPool before netClient

### Description

In the Dataproxy Go SDK, subsequent Dial calls can block forever in EnrollContext once the gnet event-loop has exited during client close, causing goroutine leaks.

### InLong Component

InLong SDK

### Are you willing to submit PR?

- [x] Yes, I am willing to submit a PR!

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)

Locate the DataProxy Go SDK close path and inspect how connPool, netClient, and the gnet event loop are shut down. Reproduce or test subsequent Dial calls through EnrollContext after client close; done means they no longer block forever or leak goroutines when the event loop has exited.

Written by the indexing model from the issue text.