hclsimple cannot parse subscribe_event_types

Input policy

```
# comment
# comment

path "some/path/*" {
capabilities = ["read", "list", "subscribe"]
subscribe_event_types = ["*"]
}
```

Result
```
policy.hcl:6,3-24: Unsupported argument; An argument named "subscribe_event_types" is not expected here.
```

Start by reproducing the policy shown in the issue through hclsimple and trace how the subscribe_event_types argument is parsed. The work is complete when this input is accepted without the reported unsupported-argument error and the relevant parsing behavior is covered by tests.

Written by the indexing model from the issue text.