The timestamp_granularities attribute is not properly getting passed to the server (Audio transcriptions)

[ben5516]

The below example is broken:

response = client.audio.transcriptions.create(
        model:                    "whisper-1",
        file:                     File.open(mp3_filepath.to_s, "rb"),
        response_format:          :verbose_json,
        timestamp_granularities:  [ :word, :segment ],
        language:                 "en"
 )

The response does not include the list of words and their timestamps. This is because timestamp_granularities is not getting properly encoded. I've created a working, corresponding fix to this issue here #249

[jbeckwith-oai]

Reproduced locally on current main (8be999ac). The multipart encoder emits two parts named timestamp_granularities, not the bracketed array key expected by the API. PR #249 targets this serializer behavior.