Enhance get_translations() to optionally return full contents

[StasNemy]

Thanks for the great work on this codebase!

I added a small enhancement to the get_translations method to optionally return the full JSON response from the API via the return_contents parameter. This makes it easier to access additional metadata (like frequencies, tags, source info, etc.) when needed, while preserving the original behavior of yielding just the terms.

Hope this is useful — let me know if you'd prefer it to return a tuple or handle this differently!