update to use new OpenAI API features, renamed engines->models, usage info in response, continue finetuning

[headchem]

• https://community.openai.com/t/api-update-engines-models/18597
• https://community.openai.com/t/usage-info-in-api-responses/18862
• https://community.openai.com/t/continue-fine-tuning-from-a-fine-tuned-model/18882