coder port-forward with IPv6 local address fails parsing

`coder port-forward` supports setting the local address like:

```
coder port-forward <workspace> --tcp 1.2.3.4:8080:8080
```

However, our parsing of this is broken for IPv6 addresses, which should be entered like `[::1]:8080:8080`. This means it's not possible to get a local IPv6 listener on localhost.

Relates to https://github.com/coder/coder/issues/14529