Gemini image generation and DeepSeek

New models

• Gemini can generate images, reachable through the OpenAI Images request format

• DeepSeek is available; its cache usage is counted under its own field names

Behaviour

• Upstream payment failures now have their own error type: no retry, and no misleading prompt to top up your own balance

• Web search counts are now collected on the Anthropic and Responses paths too