Deserialize Chunk Size in Box Responses

### Is your feature request related to a problem? Please describe.
Getting enterprise events returns chunk size but is never deserialized

### Describe the solution you'd like
The chunk size should be included in the deserialized response

Start by locating the enterprise events response deserialization entry point in the Swift SDK and inspect how the returned chunk size is handled. Confirm the response currently omits that value, then update deserialization so the chunk size is exposed in the resulting response and verify it with the relevant tests, if present.

Written by the indexing model from the issue text.