Bug on `files` upload with `expires_after`

[amaneshi]

I tried to upload file with this code (without expires_after work fine)

	params := openai.FileNewParams{
		File:    file,
		Purpose: openai.FilePurposeUserData,
		ExpiresAfter: openai.FileNewParamsExpiresAfter{
			Seconds: 30 * 24 * 60 * 60,
		},
	}
	resp, err := c.client.Files.New(ctx, params)
	if err != nil {
		return "", fmt.Errorf("failed to upload file: %w", err)
	}

and get response error

POST "https://api.openai.com/v1/files": 400 Bad Request {
    "message": "Additional properties are not allowed ('expires_after.anchor', 'expires_after.seconds' were unexpected)",
    "type": "invalid_request_error",
    "param": null,
    "code": null
  }

when I checked request details - it generate incorrect filed names (with "dot" separator), in this case

--01449e9d2956d26392006c36e9125275b6586a22f7b1526a0938c250049f
Content-Disposition: form-data; name="expires_after.anchor"


--01449e9d2956d26392006c36e9125275b6586a22f7b1526a0938c250049f
Content-Disposition: form-data; name="expires_after.seconds"

2592000
--01449e9d2956d26392006c36e9125275b6586a22f7b1526a0938c250049f

Then I checked examples, and with CURL mentioned a bit different syntax of this fields definition, so as a workaround I defined them with additional props which is worked out

	params := openai.FileNewParams{
		File:    file,
		Purpose: openai.FilePurposeUserData,
	}
	params.SetExtraFields(
		map[string]any{
			"expires_after[anchor]":  "created_at",
			"expires_after[seconds]": "2592000",  // as string, IMPORTANT!
		},
	)

and now request contain it like this and request worked as expected

--96d8b9f94995f530482d1e8884f5b46ac8dd93dbd8588fc76eeefd8c51cb
Content-Disposition: form-data; name="expires_after[anchor]"

created_at
--96d8b9f94995f530482d1e8884f5b46ac8dd93dbd8588fc76eeefd8c51cb
Content-Disposition: form-data; name="expires_after[seconds]"

2592000
--96d8b9f94995f530482d1e8884f5b46ac8dd93dbd8588fc76eeefd8c51cb--