Adjust default/initial behavior of the engine

Some defaults on DSS C-API are left for compatibility with the official OpenDSS COM implementation. Some things to consider toggling in AltDSS-Go when the first instance is created:

- `DSS.Set_AllowChangeDir(false)`: avoid changing the process working directory. Track it in the engine instead. Required for multi-threading.
- `DSS.Set_COMErrorResults(false)`: When errors occur in the engine, some arrays are filled with one or two elements (typically just `[0]`) to represent an error, besides an error number being exposed in the error interface. Since we already map the Error API in Golang, which is more general and complete, the engine can return empty arrays instead.
- `DSS.Set_AllowForms(false)`: there are no forms and the text/terminal output is usually not useful. We are not using the output callbacks either for plotting etc., since it doesn't make much sense here.